254 GUIDEBOOK OF THE WESTERN UNITED STATES 
obtained at Obsidian Butte,” on the southeast shore of Salton Sea 
11 miles northwest of Calipatria. It is interbedded with sediments 
and is the product of a volcanic eruption, probably from a cinder 
cone near the present mud volcanoes. The pumice is in pieces as 
large as 12 inches, and only those over 2 inches are shipped. The 
material is sorted by hand. There is another mine in a similar deposit 
9 miles northwest of Calipatria, in an area of about 100 acres on a low 
rounded hill 
From Niland westward the mountains on the southwest side of the 
Colorado Desert or Salton Basin become conspicuous. To the 
southwest, across Imperial Valley, the Fish Creek and Superstition 
Mountains are clearly in view. Superstition Mountain consists of a 
ridge of gray biotite granite about 750 feet high, flanked on its north 
side by Tertiary sandstone and tuff with an interbedded flow of 
vesicular basalt about 200 feet thick. To the west are the rugged 
Santa Rosa Mountains, which consist of schists and granite; beyond 
this range rise the high San Jacinto Mountains, also made up of 
crystalline rocks. These ranges are sometimes known as_ the 
Peninsular Mountains because they continue far south down the great 
peninsula of Baja California. On the north side of the railroad west of 
Niland are low ridges of sandstone and shale of late Tertiary age which 
come to the surface at Niland. (Turn to sheet 27.) 
At Mundo siding the Salton Sea is in sight (pl. 36, B), and the 
railroad skirts its north shore nearly to Mecca. It is a weird spectacle 
in the moonlight. 
In crossing the Colorado Desert and Coachella Valley from Yuma 
to Banning striking changes will be noticed in the natural vegeta- 
tion, especially near Banning, where the xerophilous (‘‘drought- 
loving’’) Lower Sonoran flora ceases. Near Yuma the desert plants 
are about the same as those in Arizona, but the sahuaro is absent. 
The ocotillo (Fouquieria splendens; see pl. 41, A) occurs near the 
ilroad as far west as a point a few miles beyond Glamis, where 
it recedes to the hillsides on the north, along which it continues to 
Red Canyon, near Mecca. The paloverde (Cercidium torreyanum) 
and indigo thorn (Parosela spinosa) continue to Palm Springs, and 
a few trees like the desert willow (Chilopsis linearis) and the mesquite 
(Prosopis glandulosa) extend part way through San Gorgonio Pass. 
The mesquite thrives in the sand dunes in the Indio and Indian 
Springs region, where a low trailing form (Prosopis juliflora) abounds. 
The beautiful Washington palm (Neowashingtoniana Jilamentosa) 
begins at the Dos Palmas Spring, north of Durmid, and occurs in 
groups | at various springs along the mountain slopes past Indio. 
— 7 Rock from from ledges in this butte has | tridymite and barbierite, probably by 
oe been cos ot gol meen obsidian, | the action of hot volcanic gases. 
ata ; mixture of | (A. F. Rogers.) 
