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.