At the Farallon light-house on Farallon Island, 30 miles west of San Francisco, the average rainfall is 18.44 inches. This may be taken as the probable average along the coast at this latitude, where the precipitation is not influenced by adjacent mountain masses. At San Francisco the annual rainfall is 22.77 inches, the increase being due to the influence of the Coast Range. Toward the east, in the Sacramento Valley, the annual rainfall is about the same as over the ocean, being 19.78 inches at Fairfield and 19.60 inches at Sacramento. Folsom is at the foot of the Sierra Nevada, at an altitude of 180 feet, and has an annual rainfall of 23.81 inches. On the western slope the rainfall increases with increase in altitude, but not uniformly. The rainfall at Auburn is 33.06 inches, at Colfax, 47.02 inches, and at Cisco, a short distance west of the summit, 51.18 inches. The increase from Folsom to Colfax is at the rate of some

what more than 1 inch per 100 feet rise in elevation, while from Colfax to Cisco the increase is at the rate of but a little more than 0.1 inch per 100 feet rise in elevation, or about one-tenth of the increase below. At Summit, on the crest of the range, the rainfall is 47.74 inches, or 3.44 inches less than at Cisco, although Summit is 1,028 feet higher. The sudden decrease in rainfall on the lee side of the range is strikingly shown in this diagram. At Summit the rainfall is 47.74 inches and at Truckee 26.35 inches. The difference in altitude of these two points is 1,197 feet and the actual decrease in rainfall is 21.39 inches, a trifle over 12 inches decrease per 100 feet drop in altitude. This rate of decrease is many times greater than the rate of increase on the opposite side of the range at the same altitude.

It is believed that the following general conclusions can be justly drawn from a study of this section:

(1) The average rainfall over the sea in the latitude of San Francisco is about 18.50 inches.

(2) On the southwest slopes of mountain ranges exposed to the storm winds the increase in rainfall is at the rate of approximately 1 inch per 100 feet rise up to an altitude of 2,500 feet.

(3) Between about 2,500 and 6,000 feet there is still an increase in the amount of rainfall, but at a much lower rate.

(4) Above 6,000 feet there is a slight decrease in the rainfall.

(5) The first high cold land passed over by the winds cools the atmosphere and condenses a large part of the moisture, leaving less or little for the land beyond.

The available rainfall records in the Salinas Valley and adjacent regions are given in the accompanying table. When these records are examined it is seen that there is a great difference in the amount of rainfall at different points-as at Mansfield and at San Ardo, for example. Fig. 2 is a graphic illustration of these variations. The section is similar to the one in fig. 1, and extends from the Pacific Ocean across the Santa Lucia Range, the Salinas Valley, and the

FIG. 2.-Diagram showing unequal distribution of rainfall in the Coast Range of California, the result of topography.

Mount Diablo Range to Fresno, on the east side of the San Joaquin Valley. The Santa Lucia Range, the most elevated land mass on the coast of central California, fronts the Pacific Ocean for more than 100 miles, exposing a bold, rugged system of peaks and ridges to the full force of the storm winds that sweep up from the southwest. Over this range these moisture-laden winds, in their passage inland, are forced to rise in altitude from 3,500 to 6,000 feet. This range, from its position and altitude, should be one of the dominant factors in the distribution of rainfall in this region, and an examination of the rainfall diagram given in fig. 2 shows that this is the case.

At Piedras Blancas light-house, near sea level, the average annual rainfall is 19.10 inches. At Point Sur light-house it is 18.11 inches. The rainfall at sea level here is apparently about the same as at Farallon light-house. In passing eastward along the line of this profile the next station is Mansfield, at an altitude of about 2,500 feet, and but 3 or 4 miles from the ocean. The average rainfall here is 49.31 inches, or more than two and one-half times greater than at sea level. The rate of increase with rise in elevation is somewhat greater here

Stations.

25

23

44

183

452

616

723

996

960

950

0

270 2,300

2,500

a U. S. Weather Bureau and Southern Pacific Railway Company.

Season

Seasonal rainfall, in inches, in the Salinas Valley and the adjacent coast region-Continued.

19.46 18.98 12.57 7.50 8.87 11.33 16.42 23.77
24.22 17.97 12.93 8.15 5.83 7.42 11.98 20.52 10.66
33.42 28.93 18.03 12.02 12.92 13.63 22.65 41.68 27.23
26.86 a 17.46 13.70 5.20 3.85 4.03 6.83 12.95 7.27

14.97

a Broken record.

than in the Sierra Nevada. There are no records at a greater elevation in this range, but the precipitation undoubtedly increases with the altitude.

The next station on this section is at Jolon, 960 feet above sea level, where the average rainfall is 18.16 inches. To the northeast, in the broad, low Salinas Valley at San Ardo, the rainfall is still less, being but 10.39 inches. On the northeast side of the Salinas Valley the Mount Diablo Range rises to an average altitude of 3,500 to 4,000 feet, and there is a noticeable increase in the rainfall over this region. At Priest Valley, altitude 2,300 feet, the annual rainfall is 19.17 inches. This is, however, but a four years' record. In passing northeastward to the San Joaquin Valley, the rainfall diminishes, being 7.83 inches at Los Banos and 8.79- inches at Fresno. If similar sections should

be drawn either to the north or south of this the same distribution of rainfall would be noted.

At Salinas the average annual rainfall is 13.70 inches, and there is a material increase to the northwest, there being 19.61 inches at Pajaro and 26.31 inches at Santa Cruz, these two stations being beyond the influence of the Santa Lucia Range. average rainfall is 15.53 inches.

At Monterey the

Feb.

Mar.

Apr.

May.

June.
July.

Aug.

Piedras Blancas L.H.

FIG. 3.-Diagram showing monthly distribution of rainfall in the Salinas Valley.

In passing up the Salinas Valley the rainfall is found to decrease as far as Soledad, where it is but 8.94 inches. To the southeast there is a steady increase, the records showing 10.39 inches at San Ardo, 10.54 inches at San Miguel, 15.25 inches at Paso Robles, and 27.78 inches at Santa Margarita.

Salirtas