the greater part of its course has a rapid fall. The upper part of the drainage basin is brush covered on steep slopes, and the valley floor is shaded by oaks. The slopes are bare on the east wail of the lower half of the basin. The valley furnishes no combination of large storage basin followed just downstream by a good dam site.a

A gaging station was established on this stream 1 mile.south.of Jolon, and a record of the discharge was kept from December 15, 1900, to April 30, 1901. From these observations the following table of discharge of San Antonio River has been prepared:

Estimated monthly discharge of San Antonio River at Jolon.

NOTE.-Gage heights and discharge measurements for 1901 are given in WaterSupply Paper No. 66, page 154. Rating table on page 178 of same paper.

During the summer of 1900 this drainage basin was explored under the direction of Prof. Charles D. Marx to discover and survey any possible reservoirs. The only one discovered on this stream is on the Pleyto ranch, 6 miles southeast of Pleyto post-office, the dam site being in sec. 30, T. 24 S., R. 10 E. (see Pl. I), and about 12 miles above the junction of San Antonio River with Salinas River.

PINKERTON RESERVOIR.

A reconnaissance survey was made of this reservoir, known as the Pinkerton site, by Prof. Charles D. Marx. The contour map of the reservoir is shown in fig. 4, and a cross section of the canyon of San Antonio River at the dam site is shown in fig. 5. The highest contour of the reservoir is at an altitude of 950 feet, as determined by aneroid observations. The area of the drainage basin tributary to the reservoir in 322 square miles. The dam as designed was to be of sandstone rubble 50 feet high, 900 feet long on top, and 500 feet long at

a MS. report of Prof. Charles D. Marx.

Feet. 950

925

900

875

the surface of the stream. The bed rock is sandstone and it is estimated to be 25 feet below the bed of the stream. Rock suitable for the construction of the dam sabe quarried within 1,000 feet of the dam.

FIG. 5.-Cross section of canyon of San Antonio River at the Pinkerton dam site.

The following table shows the estimated storage capacity and the cost of storage at this location:

Estimated storage capacity and cost of storage at Pinkerton reservoir.a

The most northern tributary of Salinas River is the Arroyo Seco, which rises on the slopes of the highest portion of the Santa Lucia Range (Pl. I). The upper valleys of this stream are far back in the range, surrounded by high mountains. This portion of the range undoubtedly receives as great a rainfall as any other locality in this region. It does not seem unreasonable to suppose that the average annual rainfall is from 30 to 50 inches.

The drainage basin of the Arroyo Seco is almost entirely made up of sharp ridges and V-shaped canyons. The western portion is well covered with brush and trees of medium size. Toward the east this growth decreases, until at the

a MS. report of Prof. Charles D. Marx,

B

Salinas the country is bare. The stream beds of this area fal' rapidly, the Arroyo Seco rising at nearly 6,000 feet and emptying into the Salinas at an elevation of 170 feet."

For 10 miles above its junction with the Salinas the channel of this stream is a broad wash of gravel and sand across the flat plain, into which the stream sinks in the dry season and from which it receives its name "Arroyo Seco." For the next 11 miles the stream flows in a deep terraced valley eroded into bituminous shales. The terraces form a most conspicuous feature (see Pl. VI and Pl. IX, 4) and mark successive periods of uplift. They were cut into the bituminous shale or sandstone by the stream.

FIG. 6.-Discharge of Arroyo Seco, Pettitt ranch, from September 1, 1901, to August 30, 1902.

The present channel of Arroyo Seco in this 11-mile section is a deep trench or canyon, from 100 to 200 feet deep and 250 to 1,000 feet wide, sunk below the floor of the valley. The bottom of this canyon is covered with great washes of granite bowlders and sand. (See Pl. VII, A.) This débris conjoins with the floods of water that rush down from the mountains above to form the agencies that are now actively eroding the channel of this stream.

A record of the discharge of this stream was kept at Pettitt ranch during 1902 and a portion of 1901. From these observations the table on page 54 has been prepared. Fig. 6 is a graphic illustration of the discharge during the season of 1901-2.

a MS. report of Prof. Charles D. Marx.