STATE GEOLOGIST. 101 
Fig. 45.—Otay Dam, San Diego, Cal. 
arched form, arching up stream with a radius of 359 feet. The maximum 
thickness at the botttom for 14 feet in height is 24 feet, decreasing in steps 
until the top 5 feet is but 4 feet thick. The proportions of concrete are 
also graded in strength from the bottom toward the top. The bottom 31 
feet is of concrete composed of I part cement, 2.1 parts sand and 3.4 
-patts crushed stone; from elevation 31 to 36 it is of 1 part cement, 3.2 
parts sand and 4.2 parts stone; from elevation 36 to 75, it is of I part 
cement, 3.33 parts sand and 4.6 parts of stone. The bottom portion is 
reinforced for water tightness with steel plates. From the point where 
the steel plates cease to the top, the dam is reinforced by horizontally 
laid steel railway cables, 114 inches in diameter, spaced 2 feet apart ver- 
tically. 
Las Ninfas Dam.—The United States Army officers built a concrete 
dam near Guatanamo, Cuba, shortly after the American-Spanish war. 
which stood a remarkably severe test a short time after its construction. 
The dam was in a narrow gorge, and was 24 feet long, 15 feet high and 2 
feet thick with a straight crest. A sudden heavy rain in the hills raised 
the water so that it passed over the dam to a depth of 10 feet upon the 
crest, no damage being done. The concrete must have acted as a beam in 
this case to have withstood such a weight of water. 
Some of the larger dams now under construction in the eastern por- 
tion of the United States are being built of concrete in which large irreg- 
