UNRAVELING EARTH HISTORY
In order to understand better the geologic history and development of the canyon, one should also have some knowledge of the basic principles of earth history and should be familiar with the [geologic time scale] ([fig. 6]).
Fig. 6. [Geologic time scale]. Reproduced from [FOSSILS]: An Introduction to Prehistoric Life, William H. Matthews III, Barnes and Noble, Inc., 1962.
[GEOLOGIC TIME SCALE] [ERA] [PERIOD] [EPOCH] SUCCESSION OF LIFE [CENOZOIC]“RECENT LIFE” QUATERNARY0-1 MILLION YEARS Recent [Pleistocene] TERTIARY62 MILLION YEARS [Pliocene] Miocene Oligocene Eocene Paleocene [MESOZOIC]“MIDDLE LIFE” CRETACEOUS72 MILLION YEARS JURASSIC46 MILLION YEARS TRIASSIC49 MILLION YEARS [PALEOZOIC]“ANCIENT LIFE” [PERMIAN]50 MILLION YEARS CARBONIFEROUS PENNSYLVANIAN30 MILLION YEARS MISSISSIPPIAN35 MILLION YEARS DEVONIAN60 MILLION YEARS SILURIAN20 MILLION YEARS ORDOVICIAN75 MILLION YEARS CAMBRIAN100 MILLION YEARS PRECAMBRIAN ERAS [PROTEROZOIC] ERA [ARCHEOZOIC] ERA APPROXIMATE AGE OF THE EARTH MORE THAN 4 BILLION 550 MILLION YEARS
The geologist has learned that the earth’s physical features have not always been as they are today. It is known, for example, that mountains now occupy the sites of ancient seas. Coal is now being mined where swamps existed many millions of years ago. Furthermore, the earth’s plants and animals have also been subject to great change. The trend of this organic change is, in general, toward more complex and advanced forms of life. However, some forms have remained virtually unaltered while others have become extinct at different points in [geologic time].
In order to interpret earth history, the earth scientist gathers evidence of the great changes in climate, geography, and life that took place in the geologic past. He does this by studying the [rock formations], the structural relationships of these formations, and the landforms of the area. The record of ancient events is pieced together by studying the stony layers of the earth as one might study a giant history book. Indeed, the [sedimentary rocks] are the rocky “pages” of earth history, for in them we find the tracks and trails, and bones and stones, which reveal the intriguing story of life long ago.
Much of the basic information which the geologist uses to reconstruct the geologic history of a region comes from his examination and interpretation of bedrock [outcrops]. Bedrock is the solid unweathered [rock] which underlies loose earth material such as soil, sand, and gravel. An outcrop, or exposure, is a place where bedrock is exposed at the surface.
The first chapter of earth history begins with the most ancient [rocks] known. Because they were formed early in [geologic time], these rocks are normally found deeply buried beneath younger rocks which have been deposited on top of them. It is for this reason that earth history is read from the bottom up, for the earliest formed rock layers correspond to the opening chapter in our earthen history book. The later chapters are found in the upper younger rocks which are located nearer the surface. Thus, in “reading” the geologic history of Palo Duro Canyon we start with the oldest “chapter” which is recorded in the Quartermaster [Formation] ([p. 17]) of [Permian] age, for these are the oldest rocks exposed in the canyon.
But deciphering earth history is not as simple as it might appear. In many areas the [rock] layers are not always found in the sequence in which they were originally deposited. In places, great structural disturbances have caused some of the rocky “pages” to become shuffled and out of place; others may be missing completely. Many rocks have been destroyed by [weathering] and erosion or greatly altered by [metamorphism]. As a result, the story recorded in these particular rocks is lost forever. These missing “pages” make the ancient story even more difficult to interpret so the geologist must then depend on other evidence that will permit him to “fill in the blanks.”
The record revealed in the [rocks] indicates that our planet is at least 4½ billion years old and that life has been present for more than 3 billion years. During this vast span of time the earth and its inhabitants have undergone many changes.
THE GEOLOGIC COLUMN AND [GEOLOGIC TIME] SCALE
The geologic column refers to the total succession of [rocks], from the oldest to the most recent, that are found in the entire earth or in a given area. For example, the geologic column of Texas includes all rock divisions known to be present in the State. By the same token, the geologic column of Palo Duro Canyon consists of the [geologic formations] exposed there. Thus, by referring to the geologic column previously determined for a specific area, the geologist can determine what type of rock he might expect to find in that particular region.
The [geologic time scale] ([fig. 6]) is composed of named intervals of [geologic time] during which were deposited the [rocks] of the geologic column. These time intervals bear the same names that are used to distinguish the various units of the geologic column. For example, one can speak of [Permian] time (referring to the geologic time scale) or of Permian rocks (referring to rock units of Permian age in the geologic column).
Both the geologic column and the [geologic time scale] are based upon the principle of [superposition]. This basic geologic concept states that unless a series of [sedimentary rock] has been overturned, a given [rock] layer is older than the [strata] above it, and younger than all of the layers below it. Thus, the field relationship of the rocks plus the type of [fossils] (if present) give the geologist some indication of the relative age of the rocks. Relative age does not imply age in years; rather, it fixes age in relation to other events that are recorded in the rocks.
Within recent years, however, it has become possible to assign ages in years to certain [rock] units. This is accomplished by a system of rock dating based on very precise measurements of amounts of radioactive elements (such as uranium). When present in the rocks, radioactive [minerals] change or decay at a known rate so that they are natural “clocks.” This method of dating has made it possible to devise a time scale in years which gives some idea of the tremendous amount of time that has passed since the oldest known rocks were formed. It has also been used to verify the previously determined relative ages of the various rock units.
The largest unit of [geologic time] is an [era], and each era is divided into smaller time units called [periods]. A period of geologic time is divided into epochs, which, in turn, may be subdivided into still smaller units. The [geologic time scale] might be roughly compared to the calendar in which the year is divided into months, months into weeks, and weeks into days. Unlike years, however, geologic time units are arbitrary and of unequal duration, and the geologist cannot be positive about the exact length of time involved in each unit. The time scale does, however, provide a standard by which he can discuss the age of [fossils] and their surrounding [rocks]. By referring to the time scale it may be possible, for instance, to state that a certain event occurred during the [Paleozoic] Era in the same sense that one might say that something happened during the American Revolution.
There are five eras of [geologic time], and each has been given a name that is descriptive of the degree of life development that characterizes that [era]. Hence, [Paleozoic] means “ancient-life” and the era was so named because of the relatively simple and ancient stage of life development.
The eras, a guide to their pronunciation, and the literal translation of each name is shown below.
[Cenozoic] (SEE-no-zo-ic)—“recent-life” [Mesozoic] (MES-o-zo-ic)—“middle-life” [Paleozoic] (PAY-lee-o-zo-ic)—“ancient-life” [Proterozoic] (PRO-ter-o-zo-ic)—“earlier-life” [Archeozoic] (AR-kee-o-zo-ic)—“beginning-life”
[Archeozoic] and [Proterozoic] [rocks] are commonly grouped together and referred to as Precambrian in age. In most places Precambrian rocks have been greatly contorted and metamorphosed, and the record of this portion of earth history is most difficult to interpret. Precambrian time represents that portion of [geologic time] from the beginning of earth history until the deposition of the earliest fossiliferous Cambrian [strata]. Precambrian time probably represents as much as 85 percent of all geologic time.
The oldest [era] is at the bottom of the time scale because this part of [geologic time] transpired first and was then followed by the successively younger eras which are placed above it. This is, of course, the order in which the various portions of geologic time occurred and during which the corresponding [rocks] were formed.
As mentioned above, each of the eras has been divided into [periods], and most of these periods derive their names from the regions in which the [rocks] of each were first studied. For example, the Pennsylvanian rocks of North America were first studied in the State of Pennsylvania.
Fig. 7. Generalized geologic map of Palo Duro Canyon State Park.
EXPLANATION Q & T[Pleistocene] and [Pliocene] undifferentiated RdoDockum Group P[Permian] undifferentiated
The [Paleozoic] [Era] has been divided into seven [periods] of geologic time. With the oldest at the bottom of the list, these periods and the source of their names are:
[Permian] (PUR-me-un)—from the Province of Perm in Russia Pennsylvanian (pen-sil-VAIN-yun)—from the State of Pennsylvania Mississippian (miss-i-SIP-i-un)—from the Upper Mississippi Valley Devonian (de-VO-ni-un)—from Devonshire, England Silurian (si-LOO-ri-un)—for the Silures, an ancient tribe of Britain Ordovician (or-doe-VISH-un)—for the Ordovices, an ancient tribe of Britain Cambrian (KAM-bri-un)—from the Latin word Cambria, meaning Wales
The Carboniferous [Period] in Europe includes the Mississippian and Pennsylvanian Periods of North America. Although this classification is no longer used in the United States, the term Carboniferous is found in many of the earlier geological publications and on many of the earlier geologic maps.
The [periods] of the [Mesozoic] [Era] and the source of their names are:
Cretaceous (cre-TAY-shus)—from the Latin word creta, meaning chalky Jurassic (joo-RAS-ik)—from the Jura Mountains of Europe Triassic (try-ASS-ik)—from the Latin word triad, meaning three
The [Cenozoic] [periods] derived their names from an old outdated system of classification which divided all of the earth’s [rocks] into four groups. The two divisions listed below are the only names of this system which are still in use:
Quaternary (kwah-TUR-nuh-ri) Tertiary (TUR-shi-ri)
Although the units named above are the major divisions of [geologic time] and of the geologic column, the geologist generally works with smaller units of the column called [geologic formations]. A geologic formation is a unit of [rock] that is recognized by certain physical and chemical characteristics. A formation is generally given a double name which indicates both where it is exposed and the type of rock that makes up the bulk of the formation. For example, the Beaumont Clay is a formation consisting of clay deposits that are found in and around Beaumont, Texas. For convenience in study, two or more successive and adjoining formations may be placed together in a group. Thus, the Tecovas and Trujillo Formations have been placed in the Dockum Group. Likewise, a formation may be subdivided into smaller units such as members, which may also be given geographic or lithologic (rock type) names.
[GEOLOGIC FORMATIONS] EXPOSED IN PALO DURO CANYON
As noted above, all of the [rocks] which crop out in Palo Duro Canyon are [sedimentary] in origin. They represent four different geological [periods]: the [Permian], Triassic, Tertiary, and Quaternary ([fig. 12]).
Although these [rock formations] differ considerably in composition and age, they do not tell the whole geologic story of the area. Long spans of [geologic time] are not represented by [rock] units because the region was undergoing erosion or no [sediments] were being deposited during certain portions of geologic time. Rocks that had formed during one geologic [period] were removed by erosion during a later period. Thus, segments of the geologic record were destroyed or never recorded. For this reason, much of the geologic history of the Palo Duro area is unrecorded and must be inferred from fragmentary evidence borrowed and pieced together from adjacent areas. Even so, an interesting story can be assembled from the rocks that remain in the canyon today.
In general, the following descriptions of the [formations] exposed in Palo Duro Canyon State Park follow the procedure that most geologists use in presenting the results of their geologic investigations. The more distinctive characteristics of the [rock] units are described in order that they may be more easily recognized, and the ways in which the rocks were formed are also considered. With this background it is then possible to review the geologic history recorded in the bedrock of the canyon. A simplified geologic map is presented in [figure 7]; this shows the distribution of the major rock types in the canyon. The reader will find it helpful to refer to this map when reading the descriptions of the various formations.
Quartermaster [Formation].—
The oldest [formation] exposed in the canyon is the Quartermaster Formation of [Permian] age (see [fig. 6]) which is named from exposures along the banks of Quartermaster Creek in Roger Mills County, Oklahoma. One of the more colorful formations in the park, the Quartermaster is composed primarily of brick-red to vermilion [shales] which are interbedded with lenses of gray shales, clays, mudstones, and [sandstones]. Averaging about 60 feet thick where exposed in the park, the Quartermaster forms the floor and lower walls of the canyon.
The [rocks] of this [formation] are easily examined at many places throughout the canyon and in them can be seen a number of interesting geologic phenomena. Probably the most noticeable of these features are the shining white veins of [gypsum] that lace the face of the red [shale] [outcrops] ([fig. 8]). A soft, transparent to translucent [mineral] that can be scratched by a fingernail, gypsum is hydrous calcium sulfate (CaSO₄·2H₂O). Three varieties of gypsum are found in the canyon: (1) satin spar, a fibrous variety with a silky sheen; (2) selenite, a colorless, transparent variety which commonly occurs in sheet-like masses; and (3) a fine-grained massive variety called alabaster. Satin spar is the most common variety of gypsum present and it commonly occurs in thin bands interbedded with the mudstones and [sandstones]. It is much more noticeable in the shales, however, for it is typically seen in narrow veins which criss-cross the surface of the outcrop and intersect the [bedding planes] at various angles. Although normally white, some of the satin spar has a soft pink or bluish hue due to the presence of impurities in the mineral.
Fig. 8. Veins of selenite [gypsum] (top arrow) in Quartermaster [Formation]. Notice diagonal [joint] to left of geologist’s hand (lower arrow).
The presence of [gypsum] in the Quartermaster [red beds] is of special significance to the geologist, for it provides valuable information about the geologic history of the Palo Duro area. It is known, for example, that when a landlocked body of sea water in an arid climate becomes separated from the ocean, one of the most common salts to precipitate is hydrous calcium sulfate, or gypsum. Gypsum may also be precipitated when a lake without an outlet evaporates in an arid climate. Geologic evidence suggests that the [sediments] which gave rise to the [rocks] of the Quartermaster [Formation] were deposited in a landlocked arm of the sea during the latter part of the [Permian] [Period]. As evaporation continued and the sea water was reduced to approximately one-third of its original volume, gypsum was precipitated. There must have been periodic influxes of [silt]- and mud-bearing waters entering the ancient Permian sea, for layers of [shale] and mudstone are interbedded with the gypsum.
It is believed that much of the satin spar and selenite [gypsum] was originally [anhydrite] (CaSO₄). Unlike gypsum, anhydrite does not contain water, but it can be changed to gypsum in the presence of moisture. There are two lines of evidence that indicate an anhydrite origin for the Quartermaster gypsum. First, microscopic examination of gypsum samples reveals the presence of residual anhydrite crystals embedded in the gypsum. Second, many of the gypsum beds have been squeezed into rather gentle folds. These consist of small [anticlines], upfolds or arches, and [synclines], downfolds or troughs ([fig. 9]). It has been suggested that this folding took place as the anhydrite underwent hydration, or took on water. As hydration occurred and the anhydrite was converted to gypsum, the gypsum expanded, thereby exerting both lateral and vertical pressure on the beds around it. This produced the crumpled, wave-like folding so characteristic of certain of the gypsum beds. However, there is not complete agreement that the folding in the gypsum is due to the hydration of anhydrite. Certain geologists attribute this deformation to slumping caused by solution cavities, for gypsum is relatively easily dissolved in water. As the gypsum was dissolved and carried away in solution, the removal of the supporting layers of gypsum permitted slumping and consequent deformation in the overlying [shales] and mudstones. Although some geologists believe that the folds were caused by expansion due to the hydration of anhydrite and others support deformation related to the removal of soluble gypsum, there is general agreement that the folding is local and not related to regional or widespread deformation.
Fig. 9. Sagging beds of Quartermaster [Formation] have produced this gentle [syncline], or downfolding, in the [rocks]. The “dome” on Capitol Peak can be seen in the background.
Not all of the red Quartermaster [shales] are uniformly colored. Some of them contain gray-green, circular spots called reduction halos ([fig. 10]). These spots, which in places give the red shales a distinctive polka-dot appearance, have been produced as the result of chemical change of certain [minerals] within the shale.
As noted earlier, [sediments] are usually laid down in horizontal layers. However, in certain environments, sediments may be deposited in such a way that the layers are inclined at angle to horizontal ([fig. 11]). This structure, called cross-bedding or cross-stratification, is found in certain [sandstones] and other coarse-grained or fragmental [sedimentary rocks]. Cross-bedding typically consists of rather distinct inclined layers separated by [bedding planes] (the surface of demarcation between two individual [rock] layers). Bedding of this type commonly occurs in sedimentary rocks formed in rivers, deltas, and along the margins of lakes or oceans. The cross-bedding in the Quartermaster and certain of the Triassic [formations] is believed to have been developed under similar conditions. Although cross-bedding is also common in certain rocks of [eolian] origin (deposited by wind) none of the cross-bedding in the canyon’s rocks is due to the action of wind.
In addition, some of the Quartermaster [strata] have [ripple marks] on their surfaces. These features are common in certain [sedimentary rocks] and were formed when the surface of a bed of [sediment] was agitated by waves or currents. The size, shape, and cross section of the ripple marks can be used to tell whether the marks were produced by waves or currents. The ripple marks in the Quartermaster appear to have been formed by the action of waves on a shallow sea floor.
A number of interesting geologic features in the canyon have been formed in part in the Quartermaster [Formation]. These include the multi-hued Spanish Skirts ([fig. 26]), the Devil’s Slide ([fig. 35]), Capitol Peak ([fig. 32]), and Catarina Cave ([fig. 27]). The latter is a rather unusual cave in that it has developed in a large mass of landslide debris divided by projecting bedrock of the Spanish Skirts. The cave has been formed by suffosian, a process whereby water enters the landslide debris on the upper slopes and follows buried channels in the landslide removing [rock] debris as it passes through. The flood water exits at the base of the landslide by means of Catarina Cave. The plan of the cave closely resembles the drainage patterns of surface gullies.
Tecovas [Formation].—
[Rocks] of the Triassic System ([fig. 6]) are well represented in Palo Duro Canyon and consist of the Tecovas and Trujillo [Formations]. These formations are part of the Dockum Group of Late Triassic age.
Having a total thickness of about 200 feet, the Tecovas (which is named from exposures found on Tecovas Creek in Potter County, Texas) consists largely of multicolored [shales]. Also present are thin layers of soft [sandstone], which are disseminated throughout the shales, and a more prominent bed of white sandstone, which marks the middle of the [formation]. The Tecovas shales overlie the Quartermaster Formation, and the lower zone of lavender, gray, and white shales forms a relatively smooth slope that is easily distinguished from the steeper slopes of gullied red-and-white-banded shales beneath them ([fig. 12]).
Fig. 10. Chemical reactions in certain of the red Quartermaster [shales] have produced reduction halos ([p. 19]) which give the [rocks] a polka-dot appearance.
Fig. 11. This boulder, located near the foot of Triassic Peak along the Sad Monkey Railroad track, exhibits the cross-bedding typical of the Trujillo [sandstones].
But the contact zone between the Tecovas and Quartermaster [shales] involves more than a mere change in color. Here is one of the missing “chapters” in the geologic history of the canyon, for part of the Late [Permian] record and all of the record of Early and Middle Triassic time are missing from the geologic column. Such gaps in the column are represented by unconformities in the [rocks]. Here the [unconformity] is an ancient erosional surface between the Tecovas [Formation] of Late Triassic age and the Late Permian Quartermaster Formation, and there are many millions of years of earth history represented in this missing “chapter” in the geologic story of Palo Duro Canyon. During this vast span of time, thousands of feet of [sediments] were probably deposited, converted into rock, and then later removed by erosion.
Near the middle of the Tecovas [Formation] there is a bed of white, crumbly (friable) [sandstone]. Averaging about 15 feet in thickness, this sandstone contains many [joints] (small crack-like fractures) along which no appreciable movement has taken place ([fig. 8]). There are two distinct sets of these joints which intersect each other at right angles. The distinctive joint patterns, the color, and the friability of this sandstone clearly differentiate it from the harder, darker, and more coarse-grained sandstones of the overlying Trujillo Formation ([p. 22]).
The upper part of the Tecovas consists of a layer of orange [shale] which overlies the middle [sandstone] unit and is in contact with the lower part of the Trujillo [Formation].
Fig. 12. Taken from the northwest rim near Coronado Lodge, this photograph shows the four major [rock] units exposed in the park: (1) The Quartermaster [Formation] which forms the lower wall and canyon floor; (2) Tecovas Formation; (3) Trujillo Formation which caps the mesas; and (4) Ogallala Formation.
The [fossils] which have been found in the Tecovas [Formation] suggest that these [rocks] were derived from [sediments] deposited in swamps and streams. Unlike the marine deposits of the Quartermaster, the rocks of the Tecovas were formed from continental deposits laid down on the land. Fossils found in the canyon include the bones and teeth of the extinct semi-aquatic reptiles known as phytosaurs ([fig. 13]) and bone and skull fragments of a primitive amphibian called Buettneria ([fig. 14]). Coprolites (the fossilized excrement of animals), pieces of petrified wood, and the teeth and bones of lungfish have also been reported from the Tecovas.
Fig. 13. The skull of this crocodile-like creature called a phytosaur is typical of the reptiles that inhabited the Palo Duro area during the Triassic [Period]. (Photograph courtesy Panhandle-Plains Historical Museum.)
A number of [minerals] including hematite, an iron mineral, and psilomelane, a barium-magnesium oxide, occur in the Tecovas. Hematite is an ore of iron and psilomelane a manganese ore, though neither of these is present in commercial quantities in the canyon.
The Tecovas also contains a number of concretions which range from a fraction of an inch to as much as 6 inches in diameter. These spherical masses are generally harder than the fine-grained shaly sands in which they are found and were thus left behind when the surrounding [rock] was eroded away. Some of these concretions are marked by cracks or veins filled with the [mineral] [calcite]. Concretions bearing this type of structure are called septaria, or septarian concretions.
[Geodes] are also found in the Tecovas [Formation]. These are rounded concretionary [rocks] with a hollow interior that is frequently lined with [mineral] crystals. Well-formed crystals of clear [calcite] have been found in many of the geodes from the Tecovas.
Among park landmarks that are characterized by the multi-hued Tecovas [strata] are the middle portion of Triassic Peak ([fig. 25]), the upper part of the Spanish Skirts ([fig. 26]), Capitol Peak ([fig. 32]), and the Devil’s Slide ([fig. 35]).
Trujillo [Formation].—
Named from [rock] exposures on Trujillo Creek in Oldham County, Texas, the Trujillo is easy to distinguish from the underlying Tecovas [Formation]. The contact is quite distinct and lies between the top of the orange Tecovas [shale] and the base of the massive-bedded, cliff-forming Trujillo [sandstone] ([fig. 25]). Although generally fine grained and thickly bedded, there are local concentrations of pebble-sized rock fragments in the Trujillo. The weathered surface of the lower sandstone is stained red or dark brown by iron oxides. However, a fresh, unweathered surface is typically gray or greenish gray in color, and careful examination of the unweathered rock reveals the presence of tiny flakes of mica.
The basal Trujillo [sandstone] is one of the most conspicuous [rock] units in the canyon and forms many of the prominent benches and mesas so typical of the Palo Duro landscape. In places the sandstone is cross-bedded ([p. 20]) and contains channel deposits of coarse sand which suggest that the [sediments] from which it was derived were deposited in ancient stream beds.
Red, maroon, and gray [shales] overlie the basal [sandstone] member of the Trujillo, and these shales are overlain by cross-bedded, coarse-grained sandstone. Another interval of varicolored shales separates the middle sandstone bed from the upper sandstone member. The middle sandstone unit is a conspicuous ledge- or cliff-forming [rock] and is medium to coarse grained and commonly cross-bedded. In most localities, the upper sandstone is overlain by a section of red and green shales which mark the uppermost limits of the Trujillo [Formation]. In places, however, this shale section has been removed by erosion and rocks of Tertiary age directly overlie the sandstone.
Although [fossils] are not common, the remains of Buettneria ([fig. 14]), leaf imprints, pieces of mineralized wood, and the scattered teeth and bone fragments of reptiles and [amphibians] have been found. Phytosaur remains, especially teeth, have also been collected from the Trujillo [sandstones].
The Indians who formerly inhabited the Palo Duro area ([p. 3]) put the [rocks] of the canyon to a number of uses. This appears to be especially true of the rather coarse-grained Trujillo [sandstones], which were commonly used for constructing primitive rock shelters. The abrasive surface of the sandstone was especially well suited for grinding grain, and mortar holes have been found in a number of places. One of these ([fig. 15]) can be seen along the tracks of the Sad Monkey Railroad ([p. 35]) near the foot of Triassic Peak. The Indians also used the clays of the Quartermaster, Tecovas, and Trujillo [Formations] to make pottery, and iron and copper [minerals] such as hematite and malachite were used to make red and green pigments for decoration and war paint.
The Trujillo [shales] and [sandstones] can be seen in a number of Palo Duro’s more spectacular geological oddities. These erosional remnants are best developed where blocks of erosion-resistant sandstone protect underlying pedestals of softer shale ([fig. 15]). This type of differential [weathering] ([p. 31]) has produced a number of interesting and unusually shaped pedestal [rocks] or “[hoodoos]” (figs. [16] and [20]). The most spectacular erosional remnant—and one that has come to be the “trademark” of Palo Duro Canyon—is the Lighthouse ([fig. 31]). The great jumble of boulders called the Rock Garden ([fig. 34]) is also composed largely of massive blocks of dislodged Trujillo sandstone. These boulders accumulated on the canyon floor as a result of landslides. In addition, the rock profile known as Santana’s Face ([fig. 28]) is a naturally sculptured profile in the Trujillo sandstone that forms the cap of Timber Mesa.
Ogallala [Formation].—
The Ogallala [Formation] is named from exposures around Ogallala in Keith County, Nebraska. There is a major [unconformity] between the Trujillo Formation of the Triassic and the overlying Ogallala Formation of [Pliocene] (Late Tertiary) age. Missing here is the geologic evidence for what may have been some of the more exciting chapters in the canyon’s history. There is no record, for example, of the Jurassic and Cretaceous [Periods] which together encompass almost 120 million years of earth history. Also missing is any evidence of what transpired during more than 90 percent of the Tertiary Period, for no [rocks] of Paleocene, Eocene, Oligocene, or Miocene age are exposed in the canyon. Together these four epochs comprise approximately 47 million years of earth history. It is impossible, of course, to determine how many geologic formations may have been formed and later eroded during the 167 million years represented by this unconformity. However, our knowledge of present-day deposition and erosion suggests that the missing geologic record undoubtedly represents many thousands of feet of rock.
Fig. 14. The skeleton of Buettneria, a large amphibian, found in Upper Triassic [strata] in the canyon. (Photograph courtesy Panhandle-Plains Historical Museum.)
The lower portion of the Ogallala [Formation] is composed of a reddish-brown, fine- to medium-grained [sandstone] that contrasts sharply with the underlying red and green [shales] that are exposed in the top of the Trujillo Formation. Much of this sandy [rock] is characterized by pebbles consisting of a variety of [igneous], [sedimentary], and [metamorphic rocks]. Because it consists of rock and [mineral] fragments of varied composition and size, this kind of [sedimentary rock] is called a [conglomerate]. The type of rock fragments found in basal Ogallala conglomerates suggests that they were transported to the Panhandle-Plains area by streams flowing southeastward from the Rocky Mountains. As these streams deposited their loads, they left behind a wide spread blanket of sand, gravel, and mud which formed an extensive alluvial plain that extended from western Nebraska to northwest Texas. Although it is less than 100 feet thick in Palo Duro Canyon, in places this great mantle of [fluvial] (stream-deposited) [sediments] is as much as 900 feet thick.
Fig. 15. The depression in this boulder is a mortar hole believed to have been used by the Indians for grinding corn.
Fig. 16. This pedestal [rock], located near the Lighthouse, is capped by a slab of weather-resistant Trujillo [sandstone].
Most of the Ogallala [Formation] consists of a mixture of diverse [rock] types such as [conglomerate], [sandstone], [siltstone], clay and marl. But the upper part of the formation is characterized by thick [caliche] deposits. A dull, earthy [calcite] deposit, caliche typically forms in areas of scant rainfall. It is believed to originate when ground moisture, containing dissolved calcium bicarbonate, moves to the surface where the moisture steadily evaporates leaving a calcium carbonate crust on or near the surface ([fig. 17]).
[Caliche], which derives its name from the Latin calix, meaning “lime,” may be firm and compact or loose and powdery. It is also commonly found mixed with other materials such as clay, sand, or gravel. Caliche commonly occurs in the Trans-Pecos, southwestern Gulf Coastal Plain, and the High Plains area of Texas (see [fig. 5], [p. 8]). In the latter area it typically makes up the “caprock.” Caliche is commonly quarried in these parts of Texas where it is used as road material and as an aggregate.
Good exposures of Ogallala [caliche] can be seen on the surface around the overlook at Coronado Lodge on the northwest rim of the canyon ([fig. 17]). Ogallala [strata] also crop out along the upper reaches of Park Road 5 as it starts to descend into the canyon. But probably the most spectacular exposures of the Ogallala are exposed in the precipitous face of the Fortress Cliff ([fig. 33]) which forms part of the eastern rim of the canyon.
Also located within the Ogallala [Formation] is a very important [aquifer]—a porous, water-bearing rock formation. This fine-to coarse-grained [sandstone] is very porous and permeable and is the most important single water-producing formation in the Panhandle-Plains area.
Fig. 17. The white surface in the right foreground consists of [caliche] ([p. 26]) in the Ogallala [Formation]. Coronado Lodge can be seen in the right background.
Opal and [chert] are locally abundant in the Ogallala conglomerates. The opal, which is found in small cavities in the [conglomerate] is not of the gem variety but it does fluoresce. [Minerals] that exhibit [fluorescence] emit visible colors when exposed to ultraviolet light. For this reason, the Ogallala opal is sought after by [rock] and mineral collectors. The chert, a flint-like variety of quartz, occurs as [nodules] in the conglomerate and in a well-developed layer near the base of the [formation]. Both of these [siliceous] ([silica]-bearing) rocks were apparently prized by the Indians, who used them to fashion knives, scrapers, projectile points, and other artifacts. The Indians also learned that flat slabs of [caliche] were ideal for lining fireplaces and to construct primitive rock shelters.
A number of [Pliocene] vertebrates have been found in the Palo Duro area. Known as the “Age of Mammals,” the Tertiary [Period] was characterized by mammals as diverse as were the reptiles of the [Mesozoic] [Era]. Among these unusual creatures were such now-extinct species as the saber-tooth cat and the elephant-like shovel-jawed mastodon ([fig. 18]). The remains of these as well as bones of giraffe-like camels, pony-sized horses, and sloths have been found in the vicinity of the canyon. The grassy plains of Pliocene time were also inhabited by large tortoises which reached lengths of up to 3 feet ([fig. 19]). Dioramas showing how these animals might have looked, as well as their actual remains, are on display in the Hall of Pre-History in the lower floor of the Panhandle-Plains Historical Museum in Canyon, 13 miles west of the park ([p. 35]).
Fig. 18. This life-size model of a shovel-jawed mastodon is typical of the now-extinct, elephant-like creatures that lived in this area during the [Pliocene] [Epoch]. (Photograph courtesy Panhandle-Plains Historical Museum.)
Fig. 19. The carapaces of giant tortoises as much as 3 feet long have been collected from [Pliocene] [rocks] in the Palo Duro area. (Photograph courtesy Panhandle-Plains Historical Museum.)
[Rocks] of the [Pleistocene].—
The youngest [rocks] in Palo Duro Canyon State Park were formed during the [Pleistocene] [Epoch] of the Quaternary [Period] of the [Cenozoic] [Era] (see [geologic time scale], [p. 11]). Pleistocene rocks are rather widespread in much of the Panhandle-Plains area and they are mostly composed of [sediments] which were deposited in stream valleys, in lakes or ponds, or by the wind. Most of the Pleistocene [strata] in the park area consist of loose deposits of [silt] and sand which were deposited by wind action. Known locally as “blow sand,” this reddish-brown, silty sand overlies the Ogallala [caliche] at most points along the canyon’s rim.