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ESTRELLA CREEK. The most eastern branch of Salinas River is Estrella Creek (see Pl. I). At a point 20 miles southeast of its junction with the Salinas the two branches of the Estrella are known as San Juan River and Cholame Creek. The San Juan drains the northeastern slopes of the San Jose Range and Cholame Creek drains the southwestern slope of the Mount Diablo Range. Between these two mountain ranges lie the elevated mesa lands of the upper Salinas Valley. This mesa region passes over into the Carriso Plain, the waters of which, however, do not flow to the sea, but toward a salt flat or salt lake which fills the lower portion of the plain. Nothing very definite is known regarding the average rainfall in this region (see table on p. 43), but it is certain that it is very light, probably less than 10 inches, over the mesa regions, which are cut off from the storm winds by the intervening Santa Lucia and San Jose ranges. It is probable that the greater portion of the water in this stream is derived from rainfall in the surrounding mountains. The area of the drainage basin of Estrella Creek is 924 square miles, and the area of the Carriso Plain is 470 square miles.
The Nacimiento is one of the large western tributaries of the Salinas, entering that stream between San Miguel and Bradley (see Pl. I). It has its sources among the highest peaks of the Santa Lucia Range, only 3 miles from the Pacific Ocean. It flows southeastward about 35 miles, receiving many small tributaries from the southwest, and emerges from the mountains after rounding the declining ridge of the Sierra de las Piedras. From this point to the Salinas it flows in a broad, sandy channel eroded in the mesa. This stream flows for 25 miles parallel with and but a few miles northeast of the crest of the range, in the belt of maximum precipitation (see fig. 2), where the average rainfall must be from 30 to 50 inches per annum. The fact that the precipitation here is great is shown by the character of the stream and the vegetation over this portion of the range. The total area of this watershed is 380 square miles, of which 300 square miles are mountainous, the remainder being rolling hills anà river valley.
The Nacimiento watershed decreases in width from 7 miles near its head to 2 at its lower end. It is 40 miles long. The upper 7 miles is mountainous, as is all that portion lying between the river and the coast divide. The valley floor averages 1 mile in width, and extends downstream 10 miles from a point 7 miles below the head. The eastern wall of the valley is the western wall of the San Antonio. The lower 25 miles of the river lies in a narrow V-shaped canyon whose sides rise 300 to 1,500 feet. The mountain slopes are covered with brush and trees. The valley floor is shaded with white oaks of great size. For the most part the bed of the river is sandy and crosswise flat, and varies in width from 50 to 400 feet. In the open valley the banks range from 15 to 40 feet in height. There are good
IRR 89-04- 4
dam sites at the mouth of Gabilan Creek, Piedras Altas, and Pebblestone Gorge, 7 miles below the Monterey County line, but there are no corresponding storage sites of value.(
The following table of discharge of Nacimiento River in March and April, 1901, has been prepared :
Estimated monthly discharge of Nacimiento River at Bryson post-office.
[Drainage area, 171 square miles.]
NOTE.--Gage heights and discharge measurements for 1901 are given in WaterSupply Paper No. 66, page 154.
This stream is torrential, with a great run-off during the rainy season, but it dwindles to a small creek by early summer. The character of the stream in June, 1902, is shown in Pl. IV, B.
SAN ANTONIO RIVER. The drainage basin of San Antonio River joins that of the Nacimiento on the northeast, and the upper 120 square miles is in a similar mountain region (Pl. I). The area of the watershed above the Pinkerton reservoir site is 322 square miles. Of this area the mountain portion, 120 square miles, probably receives an average annual rainfall of 30 to 50 inches and the elevated valleys near Jolon as much as 18 inches. This stream leaves the mountains about 6 miles above Jolon, and from there to the Salinas flows in a broad, sandy channel through wide valleys. These valleys have an altitude of from 800 to 1,200 feet and are covered with scattering oak timber (see Pl. V).
The San Antonio drainage basin is 6 miles wide from the heal for a distance of 24 miles, then for 5 miles it widens to 10 miles; in the next 5 miles it narrow3t) 3 miles, and this width continuas for 15 miles to its mouth. The valley fio): averages 11 to 2 miles wide. The southwestern wall of the valley is 5,000 fees high at the upper end, and this height falls to a few hundred feet toward the mouth. The north wall of the valley, the Santa Lucia Range, is 3,000 to 6,000 feet high. The eastern wall decreases from north to south from 2,500 feet to a few hundred feet in elevation.
The valley floor extends to the San Antonio-Arroyo Seco divide, and the main stream has a comparatively light slope. The tributaries are short, and each for
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A. SALINAS RIVER AT BRADLEY. Shows broad-topped terrace on which the town is built, and the flat-topped hills of the mesa beyond.