252 GUIDEBOOK OF THE WESTERN UNITED STATES 
shown by a very fresh fault cliff or rift in the surface (see pl. 39) and 
by occasional earthquakes. As the great river carries a heavy load 
of sediment (see p. 240), it is reasonable to believe that it would be 
able to build a delta all the way from Yuma to the head of the Gulf 
of California at a rate equal to a slow subsidence. The salt in the 
present Salton Basin ” is believed to have resulted solely from the 
evaporation of river water and of transient streams running into the 
basin. The capacity of the Salton Basin up to the lowest point in 
the delta rim to the southeast, 30 feet above sea level, an area of 
about 2,100 square miles, is 264,500 square mile feet (square miles 
1 foot deep). (Brown.) With an average annual flow at Yuma of 
26,000 square mile feet, the water of the Colorado River, if it all 
_ entered the Salton Basin, would supply this volume in about 10 years, 
but evaporation would greatly retard and possibly prevent complete 
inundation. 
The Salton Basin is in many ways similar in configuration to other 
closed basins in arid regions. The central portion is flat, and about 
its borders are alluvial slopes extending to the foot of the mountains, 
which rise very abruptly with steep rocky slopes. A few rocky buttes 
or ridges rise above the basin floor somewhat like rocky islands in the 
sea. The lower part of the basin is filled and floored with a thick body 
of sand and silt which has been penetrated by borings, some of them 
1,000 feet deep, without reaching bedrock, although they may reach 
formations of Tertiary age. The bottom of the basin is now occupied 
by Salton Sea. On the east side of the basin are the delta deposits 
of the Colorado River several hundred feet thick, which consist 
largely of fine sand and silt. Wells near Holtville are 500 to 800 feet 
deep in sand and gravel, the lower part of which may possibly be of 
3 This salt was a residue left in the | exploration of 1848 found in the bot- 
bottom of the basin by the evaporation 
of the water and was in crusts 10 to 20 
inches thick; there also were layers of 
various thickness in the mud _ below. 
Before the inundation of 1891 salt in 
considerable amount was obtained at a 
salt works in the bottom of the basin 
and shipped from old Salton sidi 
For centuries before, however, this salt 
had been utilized by the Indians. The 
fresh waters flo into the basin 
brought the salt but contained only a 
concentrated by evaporation. A 300- 
foot boring at the old salt works re- 
vealed 270 feet of hard clay below the 
salt and mud, a deposit of earlier over- 
of in. Emory in his 
small proportion, and it has been | 
tom of the basin a very shallow, highly 
saline pond less than 1 mile in length. 
An analysis of the water of Salton 
Sea made by Earl B. Working in June, 
1923 (Carnegie Inst. Washington Year- 
book 22, p. 66, 1924), shows a concen- 
tration of nearly 39,000 parts per mil- 
lion of dissolved mineral matter. This 
tion the water 
inundation in 1907 the mineral content 
of the water was only about 3,000 parts 
per million. 
