Geological Observations.— Reagan. 239 
An east and west section through Rattlesnake Butte, showing the 
displaced rock to the north. Explanation: 1, quartzyte sandstone; 2, 
volcanic ash; 3, sandstone; 4, Oligocene shales; 5, Pierre shales. 1-3 
are Loup Fork Tertiary. Altitude 3U0 teet. 
the great number of rattlesnakes found there. At any time 
in summer the "rattlers" can be seen basking" in the sun 
by the hundred. The cap rock of these buttes, as we have 
seen, is quartzyte sandstone. On the longest and highest 
butte, called Rattlesnake butte, it is very thick, and the 
strata are usually massive. This butte has had a geological 
accident in the recent past. It has been split in two along 
its longer axis, and its northern half has slid down the slope 
to the north, so that what was once the top is now the 
north face of the bluff, the rock dipping north 45 degrees. 
Thus tilted, the broken edge forms a ridge parallel to the 
remaining original top, a narrow valley occupying the in- 
tervening space. 
Another geological accident awaits this butte in the 
near future of geologic time. It will then loose its top. 
This top is very narrow, ten to twenty feet wide and already 
has a clip of ten degrees toward the north, while the strata 
immediately underneath dip south. 
Minerals. 
So far as the writer knows there are no minerals in the 
region worth mentioning, he not having paid any attention 
to minerals in his investigations. He believes, however, 
that the Miocene (Oligocene) shales which the Indians use 
in plastering might prove of value in the making of cement. 
Resides this possibility of the clays (shales) being of value, 
placer gold is said to exist in the gravels at the mouth of 
Oak creek.* 
* Some volcanic asli was noticed at several places, but the qualitj 
and quantity were not determined. 
