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292 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

partly because of successive overlap of lower parts of the formation consists chiefly of conglomeratic sand
the formation by beds higher in the formation. An stone interbedded with relatively minor amounts of
unconformity at the base of the overlying Pico forma siltstone and mudstone. Figure 52 shows the basal
tion truncates strata of the Towsley formation near part of the Towsley formation where it rests on quartz
Elsmere and Whitney Canyons. diorite on the divide between Elsmere and Whitney
From Whitney Canyon south to Grapevine Canyon Canyons. The lowest part of the Towsley formation
the basal beds of the Towsley formation lie directly on here consists of large, closely spaced blocks of quartz
pre-Cretaceous igneous and metamorphic rocks. The diorite. The interstices between blocks are filled with
crystalline rocks near the contact generally show no sand and rounded pebbles and cobbles of a variety of
evidence of pre-Towsley weathering. The degree of rock types. Lying above the basal rubble are lenticular
fracturing in the crystalline rocks is not perceptibly beds of conglomerate and sandstone. The upper beds
more intense near the contact than at places farther overlap the rubble and rest directly on the quartz dio
away. The surface of contact is jagged in detail but rite in the upper part of the figure. At some places,
local relief on the surface is generally not greater than particularly in the area near the southeast corner of
1 or 2 feet. Viewed more broadly, the contact is very section 18, T. 3 N., R. 15 W., mound-shaped lenses of
eVen. light-gray hard calcareous fine-grained sandstone occur
At most places the basal bed of the Towsley forma near the base of the formation. They are a few yards
tion is a well-indurated conglomerate containing, in in diameter, as much as 10 feet thick, and interfinger
addition to well-rounded clasts of a great variety of with softer sandstone and pebbly sandstone beds.
rock types, angular blocks of crystalline rock of very Erosion of the softer beds has left some of the hard
local derivation. In Elsmere Canyon the coarse basal lenses standing as prominent knobs. The lenses are
beds are about 15 feet thick; in places in Grapevine generally very fossiliferous; specimens of Lucinoma an
Canyon the conglomerate or breccia is only a few inches nulata (Reeve), identified by Winterer, are particularly
thick and is overlain by fine-grained silty sandstone. abundant.
In Whitney Canyon and on the divide between Whitney In Elsmere Canyon the lower conglomeratic beds are
and Elsmere Canyons the entire exposed thickness of overlain by a sequence about 150 feet thick of fossilif

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FIGURE 52.-Contact of Towsley formation (Tt) with quartz diorite of pre-Cretaceous basement complex (Bc.) on ridge between Whitney and
Elsmere Canyons.