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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.a

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, A) and mark successive periods of uplift. They were cut into the bituminous shale or sandstone by the stream.

Sept. Oct. Nov. Dec. Jan Feb Mar Apr May June July Aug. Acre-feet.

22.000

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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.

Estimated monthly discharge of Arroyo Seco at Pettitt ranch.

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January
February
March
April
May
June
July
August
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1902.
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August
September
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1903.
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1. 11

145
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NOTE.-Gage heights and discharge measurements for 1901 are given in WaterSupply Paper No. 66, page 156. Rating table on page 178, same paper.

During the summer of 1900 the drainage area of Arroyo Seco was explored by Prof. Charles D. Marx. Three reservoir sites were discovered on Arroyo Seco—The Pools site, the Foster site, and the Currier site (Pl. I). Two sites were also discovered on Los Vaqueros Creek, a tributary of Arroyo Seco—the Pettitt site and the Leigh site. The Foster and Currier reservoir sites were resurveyed by the writer in the summer of 1902. These reservoir sites will be described in detail.

THE POOLS RESERVOIR.

The Pools reservoir site is far back in the Santa Lucia Mountains, just below the junction of Arroyo Seco and Santa Lucia Creek (Pl. I).

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It is about 20 miles west of Soledad. A reconnaissance survey was made of this reservoir site by Prof. Charles D. Marx in the summer of 1900. A contour map of the reservoir forms fig. 7, and a cross section of the canyon of Arroyo Seco at the dam site is given in fig. 8. The highest contour of the reservoir is at an altitude of 1,000 feet, as determined by aneroid observations. The drainage area tributary to the reservoir is 74 square miles of steep mountain slopes covered with thick brush and trees.

The dam as designed was to be of granite rubble, with a maximum

height of 100 feet and 250 feet long on top. The bed rock is granite and the estimated depth to solid rock is 5 feet. The following table shows the storage capacity and cost of storage at this location.

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Fig. 8.-Cross section of canyon of Arroyo Seco at The Pools dam site.

Estimated storage capacity and cost of storage at The Pools reservoir, a

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The reservoir is merely a steep, V-shaped canyon. The cost of storage, $175 per acre-foot, is prohibitive, and with the great distance, 20 miles from irrigable land, serves to condemn this location.

PETTITT RESERVOIR.

The Pettitt reservoir is in sec. 20, T. 19 S., R. 6 E., M. D. M., at the mouth of Los Vaqueros Creek. It is about 11 miles south of Sole

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FIG. 9.-Reconnaissance map of Pettitt reservoir site. dad. (See Pl. I.) A reconnaissance survey was made of this reservoir site by Prof. Charles D. Marx in the summer of 1900. A contour

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

map of the reservoir forms fig. 9, and a cross section of the canyon of Los Vaqueros Creek at the dam site is given in fig 10.

The highest contour of the reservoir has an altitude of 450 feet, as determined by aneroid observations. The area of the drainage basin tributary to the reservoir is 28 square miles. The dam as designed

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was to be a concrete masonry structure 115 feet high and 175 feet long on top. The bed rock is shale, and the estimated depth to solid rock is 5 feet.

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

Estimated storage capacity and cost of storage at Pettitt reservoir, a

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The Leigh reservoir site is in sec. 9, T. 20 S., R. 6 E., M. D. M., in Los Vaqueros Valley, 4 miles south of the Pettitt site (Pl. I).

A reconnaissance survey was made of this reservoir site by Prof. Charles D. Marx in the summer of 1900. A contour map of the reservoir forms fig. 11, and a cross section of the canyon of Los Vaqueros Creek at the dam site is given in fig. 12.

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