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.