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.