SOUTHERN PACIFIC LINES 253 
Tertiary age. In the western or upper part of the basin there is 
much coarse material and sand deposited by streams from the adjoin- 
ing steep mountain slopes. In places the sands are blown into dunes, 
which occupy areas of considerable extent. 
The beach line of the large prehistoric water body known as Lake 
Cahuilla “ is plainly visible at many places along the margin of the 
Salton Basin and extending up the Coachella Valley * to a point 
about 2 miles above Indio; it extends along both sides of Imperial 
Valley and southward into Mexico. The surface of the water was 
about 40 feet above the present sea level, or more than 310 feet 
above the bottom of the basin. Variation in elevation of the old 
beach from 30 to 57 feet above sea level indicates warping of the basin 
in recent time. In most places the old beach forms a sandy ridge or 
bench only a few feet high. West of Brawley this bench is half a 
mile wide, and 4 miles east of Niland, near the point where it is 
crossed by the railroad, it attains considerable prominence, and it 
continues in view to a point beyond Frink. Many fossil shells of 
fresh-water habit (including Anodonta, Planorbis, Physa, and Tryonia) 
occur in the sand. Near Fish Springs, on the south side of the 
basin opposite Salton siding, the old strand is marked by a band of 
white travertine, a fresh-water deposit of calcium carbonate, on the 
schists. This band is very conspicuous on a projection of the moun- 
tain known as Travertine Point (pl. 38, B) and encircling an isolated 
hill of granite 2 miles northwest of Fish Springs. The inundation of 
1907 extended to the foot of the point, covering the old trail with 
more than 60 feet of water, but it fell far short of the ancient lake 
margin marked by the travertine. Macdougal * has estimated 
that the date of the last filling of Lake Cahuilla corresponding to the 
old beach was not more than 300 or 400 years ago. The local Indians 
have traditions of the lake which disappeared “poco & poco.” Prob- 
ably there were oscillations when freshets refilled it, a process which 
may have recurred at various times while the delta was being built. 
Near the mouth of the Alamo River, on the southeast shore of the 
Salton Sea about 8 miles southwest of Niland, the presence of a center 
of voleanic activity is shown by ridges of lava pumice and active 
“volcanoes” of hot mud emitting sulphurous steam. One of these 
features is shown in Plate 38, A. There are other larger ones 75 
miles farther south, near Volcano Lake, in Mexico. Pumice is 
7 The name Coachella is probably a 
isspelling of “‘conchilla” (Spanish for 
™ This name applied to the former 
water body by W. P. Blake is that of | 
valley 
the Indians who inhabited 
on several sm 
Mecca, Cabazon, and Palm Springs. 
little shell), which was used in the early 
days and printed on the earliest 3 
76 ugal, D. T., A decade of the 
Salton Sea: Geog. Rev., vol. 3, pp. 457- 
| 473, 1917. 
