Report on the Lands of the Arid Region

Chapter III The Rainfall of the Western Portion of the United States

The Smithsonian Institution conducted for a number of years an extensive system of measurements of rainfall in the United States, and at the same time diligently collected pluvial records from every possible source. The accumulated data thus collected were placed in the hands of Mr. Charles A. Schott for reduction and discussion, and he prepared the “Smithsonian Tables of Precipitation in Rain and Snow”, which appeared in 1868. Since that time much additional material has been acquired by the continuation of the work to the present time, and also by a great increase in the number of observation stations, and so valuable is this new material that it has been determined to recompile the tables and issue a second edition. By the time the present report was called for, the preliminary computations for the tables had developed an important body of facts bearing on the climate of the Arid Region, and through the courtesy of Prof. Joseph Henry, Secretary of the Smithsonian Institution, and of Mr. Schott, they were placed at my disposal. Mr. Schott also made such a change in the order of computation as to give precedence to the states and territories which form the subject of this investigation, and by this timely favor made it possible to base the following discussion on the very latest determinations of rainfall.

The results thus made available exhibit the mean precipitation at each station of observation west of the Mississippi River for each month, for each season, and for the year. A number of other data are also tabulated, including the latitude, longitude, and altitude of each station, and the extent of each series of observations in years and months. In selecting material for the present purpose the shorter records were ignored. The variations from year to year are so great that an isolated record of a single year is of no value as an indication of the average rainfall. The mean of two or three years is almost equally liable to mislead, and only a long series of observations can afford accurate results. In the following tables no stations are included (with one exception) which show records of less than five years’ extent.

Table I shows the precipitation of the Sub-humid Region; Table II, of the Arid Region; Table III, of the San Francisco Region; and Table IV, of the Region of the Lower Columbia. The limits of each region have been given in a former chapter, and need not be repeated. In each table the first column contains the names of the stations of observation; the second, their latitudes; the third, their longitudes (west from Greenwich); and the fourth, their altitudes in feet above the level of the sea. The next four columns show for each season of the year the mean observed rainfall in inches, and their sum appears in the following column as the mean yearly rainfall. In the last column the extent of each series of observations is given in years and months. In Table I the stations are arranged by latitudes, in Tables II, III, and IV, alphabetically.

Table I.—Precipitation of Sub-humid Region.

Station.	Latitude.	Longitude.	Height.	Mean precipitation, in inches.					Extent of record.
				Spring.	Summer.	Autumn.	Winter.	Year.
	° ´	° ´	Feet.						Y. M.
Pembina, Dak	48 57	97 03	768	4.02	7.24	2.71	1.53	15.50	4 8
Fort Totten, Dak	47 56	99 16	1,480	5.18	7.17	2.50	1.59	16.44	5 5
Fort Abercrombie, Dak	46 27	96 21	—	4.80	8.67	3.46	1.85	18.78	13 6
Fort Wadsworth, Dak	45 43	97 10	1,650	7.00	10.25	3.98	2.92	24.15	6 5
Omaha Agency, Nebr	42 07	96 22	—	8.21	8.70	5.77	2.90	25.58	5 2
Fort Kearney, Nebr	0 38	98 57	2,360	7.81	11.13	4.83	1.45	25.22	14 4
Fort Riley, Kans	39 03	96 35	1,300	5.49	10.48	5.92	2.63	24.52	20 10
Fort Hays, Kans	38 59	99 20	2,107	6.93	6.23	5.77	3.77	22.70	6 11
Fort Larned, Kans	38 10	98 57	1,932	5.17	9.63	4.95	1.67	21.42	10 9
Fort Belknap, Tex	33 08	98 46	1,600	6.41	9.44	8.34	3.86	28.05	5 10
Fort Griffin, Tex	32 54	99 14	—	4.95	6.25	6.14	4.17	21.51	5 3
Fort Chadbourne, Tex	31 58	100 15	2,020	5.77	6.53	7.06	3.52	22.88	8 7
Fort McKavett, Tex	30 48	100 08	2,060	5.21	6.71	7.81	4.22	23.95	9 7
New Braunfels, Tex	29 42	98 15	720	7.60	6.90	8.83	4.25	27.58	5 1
Fort Clark, Tex	29 17	100 25	1,000	4.14	7.57	6.55	4.35	22.61	12 5
Fort Inge, Tex	29 10	99 50	845	5.38	9.67	6.88	3.53	25.46	7 4
Fort Duncan, Tex	28 39	100 30	1,460	3.56	8.60	6.54	2.63	21.33	11 7
Fort Brown, Tex	25 50	97 37	50	3.18	7.64	13.02	4.04	27.88	15 0

Table II.—Precipitation of the Arid Region.

Station.	Latitude.	Longitude.	Height.	Mean precipitation, in inches.					Extent of record.
				Spring.	Summer.	Autumn.	Winter.	Year.
	° ´	° ´	Feet.						Y. M.
Albuquerque, N. Mex	35 06	106 38	5,032	0.83	4.35	2.04	0.89	8.11	12 2
Camp Bowie, Ariz	32 10	109 30	4,872	1.29	7.35	2.03	4.59	15.26	6 8
Camp Douglas, Utah	40 46	111 50	5,024	7.20	2.18	3.24	6.20	18.82	10 3
Camp Grant, Ariz	32 54	110 40	4,833	2.08	6.25	3.27	3.48	15.08	6 10
Camp Halleck, Nev	40 49	115 20	5,790	3.66	1.19	2.31	3.82	10.98	5 8
Camp Harney, Oreg	43 00	119 00	—	2.29	1.09	1.59	3.79	8.76	6 0
Camp Independence, Cal	36 50	118 11	4,800	1.09	0.35	0.62	4.54	6.60	8 2
Camp McDermitt, Nev	41 58	117 40	4,700	3.02	0.72	1.13	3.66	8.53	6 4
Camp McDowell, Ariz	33 46	111 36	—	1.11	4.79	1.73	3.82	11.45	8 2
Camp Mohave, Ariz	35 02	114 36	604	0.81	1.27	0.93	1.64	4.65	9 1
Camp Verde, Ariz	34 34	111 54	3,160	1.25	4.65	2.41	2.54	10.85	6 1
Camp Warner, Oreg	42 28	119 42	—	4.31	1.10	2.53	6.47	14.41	5 3
Camp Whipple, Ariz	34 27	112 20	5,700	3.88	8.07	2.15	5.18	19.28	7 5
Cantonment Burgwin, N. Mex	36 26	105 30	7,900	1.57	2.92	2.42	1.74	8.65	5 9
Drum Barracks, Cal	33 47	118 17	32	2.26	0.26	0.35	5.87	8.74	5 5
Denver, Colo	39 45	105 01	5,250	5.02	3.69	3.16	1.90	13.77	5 1
Fort Bayard, N. Mex	32 46	108 30	4,450	1.54	7.22	2.28	3.28	14.32	7 6
Fort Benton, Mont	47 50	110 39	2,730	5.34	4.48	1.65	1.79	13.26	7 1
Fort Bidwell, Cal	41 50	120 10	4,680	4.95	1.54	3.03	10.71	20.23	8 3
Fort Bliss (El Paso), Tex	31 47	106 30	3,830	0.43	3.49	3.38	1.23	8.53	14 3
Fort Boisé, Idaho	43 40	116 00	1,998	5.16	1.15	2.50	6.67	15.48	9 5
Fort Bridger, Wyo	41 20	110 23	6,656	2.99	2.05	1.68	1.71	8.43	12 10
Fort Buford, Dak	48 01	103 58	1,900	3.76	4.06	2.01	2.01	11.84	7 10
Fort Colville, Wash	48 42	118 02	1,963	3.63	3.04	2.56	4.83	14.06	11 0
Fort Craig, N. Mex	33 38	107 00	4,619	0.70	5.87	3.43	1.06	11.06	15 9
Fort D. A. Russell, Wyo	41 12	104 50	—	4.76	4.56	3.27	1.50	14.09	5 1
Fort Davis, Tex	30 40	104 07	4,700	1.84	8.76	4.72	1.80	17.12	8 11
Fort Defiance, Ariz	35 43	109 10	6,500	2.03	5.91	3.72	2.55	14.21	8 5
Fort Fetterman, Wyo	42 50	105 29	4,973	4.48	4.12	2.99	3.51	15.10	5 7
Fort Fillmore, N. Mex	32 14	106 42	3,937	0.48	4.16	3.02	0.76	8.42	8 3
Fort F. Steele, Wyo	41 47	106 57	6,841	4.57	3.48	3.05	4.28	15.38	5 5
Fort Garland, Colo	37 25	105 40	7,864	3.28	6.70	2.37	2.51	14.86	13 1
Fort Lapwai, Idaho	46 18	116 54	2,000	4.11	2.41	3.38	4.99	14.89	9 8
Fort Laramie, Wyo	42 12	104 31	4,472	5.35	4.40	2.73	1.97	14.45	17 8
Fort Lyon, Colo	38 08	102 05	4,000	4.33	5.44	2.30	0.49	12.56	7 9
Fort Massachusetts, Colo	37 32	105 23	8,365	3.12	5.56	6.28	2.27	17.23	5 1
Fort McPherson, Nebr	41 00	100 30	3,726	6.90	7.56	3.25	1.25	18.96	6 9
Fort McIntosh, Tex	27 35	99 48	806	3.22	6.56	5.38	2.35	17.51	14 7
Fort McRae, N. Mex	33 18	107 03	4,500	2.43	6.15	2.32	0.69	11.59	5 0
Fort Randall, Dak	43 01	98 37	1,245	4.72	6.22	3.40	1.18	15.52	15 6
Fort Rice, Dak	46 32	100 33	—	3.63	4.87	1.54	1.35	11.39	6 1
Fort Sanders, Wyo	41 17	105 36	7,161	3.55	4.15	2.33	1.43	11.46	6 10
Fort Selden, N. Mex	32 23	106 55	—	0.58	4.83	1.86	1.22	8.49	8 5
Fort Shaw, Mont	47 30	111 42	6,000	2.18	2.30	1.34	1.13	6.95	7 3
Fort Stanton, N. Mex	33 29	105 38	5,000	3.03	10.61	4.86	2.44	20.94	7 9
Fort Stevenson, Dak	47 36	101 10	—	3.41	4.97	2.15	1.31	11.84	6 2
Fort Stockton, Tex	30 20	102 30	4,950	1.24	5.66	3.31	1.29	11.50	5 8
Fort Sully, Dak	44 50	100 35	1,672	6.52	7.18	1.70	1.14	16.54	7 8
Fort Union, N. Mex	35 54	104 57	6,670	2.12	11.92	3.79	1.32	19.15	17 5
Fort Walla Walla, Wash	46 03	118 20	800	4.69	2.07	4.98	7.62	19.36	8 8
Fort Wingate, N. Mex	35 29	107 45	6,982	1.96	6.50	3.42	5.44	17.32	9 1
Fort Yuma, Cal	32 44	114 36	200	0.27	1.30	1.36	0.98	3.91	16 6
Ringgold Barracks, Tex	26 23	99 00	521	3.71	7.00	6.31	2.58	19.60	14 2
Salt Lake City, Utah	40 46	111 54	4,534	6.25	6.28	4.71	7.57	24.81	9 2
San Diego, Cal	32 42	117 14	150	1.89	0.36	1.89	5.17	9.31	24 2
Santa Fé, N. Mex	35 41	106 02	6,846	2.17	6.82	3.45	2.47	14.91	19 10

Table III.—Precipitation of the San Francisco Region.

Station.	Latitude.	Longitude.	Height.	Mean precipitation, in inches.					Extent of record.
				Spring.	Summer.	Autumn.	Winter.	Year.
	° ´	° ´	Feet.						Y. M.
Alcatraz Island	37 49	122 25	—	2.59	0.01	1.85	12.04	16.49	9 5
Angel Island	37 51	122 26	30	3.52	0.02	2.75	12.29	18.58	5 11
Benicia Barracks	38 03	122 09	64	4.10	0.13	2.28	8.39	14.90	18 3
Fort Miller	37 00	119 40	402	7.25	0.00	2.94	8.81	19.00	6 9
Fort Point	37 48	122 29	27	3.66	0.03	2.28	11.39	17.36	14 11
Monterey	36 37	121 52	40	4.43	0.26	2.24	8.78	15.71	12 3
Sacramento	38 34	121 26	81	5.55	0.09	2.76	10.84	19.24	18 3
San Francisco; Presidio	37 47	122 28	150	4.80	0.49	2.68	12.32	20.29	20 2
San Francisco	37 48	122 25	130	5.03	0.22	3.05	13.19	21.49	24 4

Table IV.—Precipitation of the Region of the Lower Columbia.

Station.	Latitude.	Longitude.	Height.	Mean precipitation, in inches.					Extent of record.
				Spring.	Summer.	Autumn.	Winter.	Year.
	° ´	° ´	Feet.						Y. M.
Astoria, Oreg	46 11	123 48	52	18.90	5.72	18.19	34.80	77.61	22 4
Cape Disappointment, Wash	46 17	124 03	30	14.97	5.97	20.46	29.84	71.24	5 9
Fort Dalles, Oreg	45 33	120 50	350	3.91	1.16	5.78	11.27	22.12	12 8
Camp Gaston, Cal	41 01	123 34	—	14.76	1.15	9.92	31.56	57.39	12 0
Camp Wright, Cal	39 48	123 17	—	8.26	0.27	8.17	27.27	43.97	9 8
Fort Crook, Cal	41 07	121 29	3,390	6.37	0.97	4.55	11.29	23.18	9 0
Fort Hoskins, Oreg	45 06	123 26	—	14.69	2.65	14.88	34.48	66.70	6 9
Fort Humboldt, Cal	40 45	124 10	50	9.36	0.73	6.49	18.73	35.31	11 2
Fort Jones, Cal	41 36	122 52	2,570	5.23	0.91	4.19	11.37	21.70	5 0
Fort Steilacoom, Wash	47 11	122 34	300	8.98	2.81	10.12	17.01	38.92	12 9
Fort Stevens, Oreg	46 12	123 57	—	17.67	7.88	18.21	34.81	78.57	6 5
Fort Umpqua, Oreg	43 42	124 10	8	16.83	2.86	15.64	32.08	67.41	5 10
Fort Vancouver, Wash	45 40	122 30	50	8.70	3.78	9.17	16.72	38.37	16 11
Fort Yamhill, Oreg	45 21	123 15	—	13.10	2.39	13.20	26.90	55.59	9 3
Portland, Oreg	45 30	122 36	45	13.75	2.50	11.31	19.64	47.20	7 0
Port Townsend, Wash	48 07	122 45	8	5.45	4.22	2.31	4.07	16.05	5 6
San Juan Island, Wash	48 28	123 01	150	5.01	4.60	7.89	10.84	28.34	9 4

Distribution of Rain Through the Year

In a general way the limit of agriculture without irrigation, or “dry farming”, is indicated by the curve of 20 inches rainfall, and where the rainfall is equally distributed through the year this limitation is without exception. But in certain districts the rainfall is concentrated in certain months so as to produce a “rainy season”, and wherever the temperature of the rainy season is adapted to the raising of crops it is found that “dry farming” can be carried on with less than 20 inches of annual rain. There are two such districts upon the borders of the Arid Region, and within its limits there may be a third.

First District.—Along the eastern border of the Arid Region a contrast has been observed between the results obtained at the north and at the south. In Texas 20 inches of rain are not sufficient for agriculture, while in Dakota and Minnesota a less amount is sufficient. The explanation is clearly developed by a comparison of the tables of rainfall with reference to the distribution of rain in different seasons.

Table V.—Precipitation of Texas.

Station.	Latitude.	Longitude.	Height.	Mean precipitation, in inches.					Extent of record.
				Spring.	Summer.	Autumn.	Winter.	Year.
	° ´	° ´	Feet.						Y. M.
Austin	30 17	97 44	650	8.61	7.94	10.74	6.23	33.52	18 8
Camp Verde	30 00	99 10	1,400	6.11	9.81	8.30	5.05	29.27	5 9
Fort Belknap	33 08	98 46	1,600	6.41	9.44	8.34	3.86	28.05	5 10
Fort Bliss (El Paso)	31 47	106 30	3,830	0.43	3.49	3.38	1.23	8.53	14 3
Fort Brown	25 50	97 37	50	3.18	7.64	13.02	4.04	27.88	15 0
Fort Chadbourne	31 58	100 15	2,020	5.77	6.53	7.06	3.52	22.88	8 7
Fort Clark	29 17	100 25	1,000	4.14	7.57	6.55	4.35	22.61	12 5
Fort Davis	30 40	104 07	4,700	1.84	8.76	4.72	1.80	17.12	8 11
Fort Duncan	28 39	100 30	1,460	3.56	8.60	6.54	2.63	21.33	11 7
Fort Griffin	32 54	99 14	—	4.95	6.25	6.14	4.17	21.51	5 3
Fort Inge	29 10	99 50	845	5.38	9.67	6.88	3.53	25.46	7 4
Fort Mason	30 40	99 15	1,200	6.36	10.44	8.22	3.96	28.98	5 1
Fort McIntosh	27 35	99 48	806	3.22	6.56	5.38	2.35	17.51	14 7
Fort McKavett	30 48	100 08	2,060	5.21	6.71	7.81	4.22	23.95	9 7
Fort Stockton	30 20	102 30	4,950	1.24	5.66	3.31	1.29	11.50	5 8
Galveston	29 18	94 47	30	13.15	14.90	16.83	12.19	57.07	6 1
Gilmer (near)	32 40	94 59	950	13.36	9.93	11.77	10.93	45.99	7 9
New Braunfels	29 42	98 15	720	7.60	6.90	8.83	4.25	27.58	5 1
Ringgold Barracks	26 33	99 00	521	3.71	7.00	6.31	2.58	19.60	14 2
San Antonio	29 25	98 25	600	6.77	8.91	9.30	6.32	31.30	10 2
Means				4.62	6.78	6.64	3.69	21.73	— —

Table VI.—Precipitation of Dakota.

Station.	Latitude.	Longitude.	Height.	Mean precipitation, in inches.					Extent of record.
				Spring.	Summer.	Autumn.	Winter.	Year.
	° ´	° ´	Feet.						Y. M.
Fort Abercrombie	46 27	96 21	—	4.80	8.67	3.46	1.85	18.78	13 6
Fort Buford	48 01	103 58	1,900	3.76	4.06	2.01	2.01	11.84	7 10
Fort Randall	43 01	98 37	1,245	4.72	6.22	3.40	1.18	15.52	15 6
Fort Rice	46 32	100 33	—	3.63	4.87	1.54	1.35	11.39	6 1
Fort Stevenson	47 36	101 10	—	3.41	4.97	2.15	1.31	11.84	6 2
Fort Sully	44 50	100 35	1,672	6.52	7.18	1.70	1.14	16.54	7 8
Fort Totten	47 56	99 16	1,480	5.18	7.17	2.50	1.59	16.44	5 5
Fort Wadsworth	45 43	97 10	1,650	7.00	10.25	3.98	2.92	24.15	6 5
Pembina	48 57	97 03	768	4.02	7.24	2.71	1.53	15.50	4 8
Means				4.78	6.74	2.61	1.65	15.78	—

Table V includes every station in Texas that has a record of five years or more, in all twenty stations. If the means of rainfall for the state be compared with the means for single stations, it will be seen that there is a general correspondence in the ratios pertaining to the different seasons, so that the former can fairly be considered to represent for the state the distribution through the year. Table VI presents the data for Dakota in the same way, and the correspondence between the general mean and the station mean is here exceedingly close. At each of the nine stations, the greatest rainfall is recorded in summer, the next greatest in spring, and the least in winter. Placing the two series of results in the form of percentages, they show a decided contrast:

	Spring.	Summer.	Autumn.	Winter.	Year.
Dakota	30	43	17	10	100
Texas	21	31	31	17	100

In Dakota a rainy season is well marked, and 73 per cent. of the rain falls in spring and summer, or at the time when it is most needed by the farmer. In Texas only 52 per cent. of the rain falls in the season of agriculture. The availability of rain in the two regions is therefore in the ratio of 73 to 52, and for agricultural purposes 20 inches of rainfall in Texas is equivalent to about 15 inches in Dakota.

For the further exhibition of the subject, Table VII has been prepared, comprising stations in the Region of the Plains all the way from our northern to our southern boundary. By way of restricting attention to the practical problem of the limit of “dry farming”, only those stations are admitted which exhibit a mean annual rainfall of more than 15 and less than 25 inches. The order of arrangement is by latitudes, and in the columns at the right the seasonal rainfalls are expressed in percentages of the yearly. The column at the extreme right gives the sum of the spring and summer quotas, and is taken to express the availability of the rainfall.

Table VII.—Seasonal precipitation in the Region of the Plains.

Station.	Latitude.	Extent of Record.	Mean yearly rainfall.	Percentage of annual rainfall.
				Spring.	Summer.	Autumn.	Winter.	Spring and Summer.
	° ´	Y. M.	Inches.
Pembina, Dak.	48 57	4 8	15.50	26	47	17	10	73
Fort Totten, Dak.	47 56	5 5	16.44	31	44	15	10	75
Fort Abercrombie, Dak.	46 27	13 6	18.78	26	46	18	10	72
Fort Wadsworth, Dak.	45 43	6 5	24.15	29	42	17	12	71
Fort Sully, Dak.	44 50	7 8	16.54	39	44	10	7	83
Sibley, Minn.	44 30	7 11	24.74	21	40	29	10	61
Fort Randall, Dak.	43 01	15 6	15.52	30	40	22	8	70
Fort McPherson, Nebr.	41 00	6 9	18.96	36	40	17	7	76
Fort Riley, Kans.	39 03	20 10	24.52	22	43	24	11	65
Fort Hays, Kans.	38 59	6 11	22.70	31	27	25	17	58
Fort Larned, Kans.	38 10	10 9	21.42	24	45	23	8	69
Fort Griffin, Tex.	32 54	5 3	21.51	23	29	29	19	52
Fort Chadbourne, Tex.	31 58	8 7	22.88	25	29	31	15	54
Fort McKavett, Tex.	30 48	9 7	23.95	22	28	32	18	50
Fort Davis, Tex.	30 40	8 11	17.12	11	51	28	10	62
Fort Clark, Tex.	29 17	12 5	22.61	18	34	29	19	52
Fort Duncan, Tex.	28 39	11 7	21.33	17	40	31	12	57
Fort McIntosh, Tex.	27 35	14 7	17.51	18	38	31	13	56
Ringgold Barracks, Tex.	26 23	14 2	19.60	19	36	32	13	55

The graduation of the ratios from north to south is apparent to inspection, but is somewhat irregular. The irregularity, however, is not greater than should be anticipated from the shortness of the terms of observation at the several stations, and it disappears when the stations are combined in natural groups. Dividing the whole series into three groups, as indicated by the cross lines in Table VII, and computing weighted means of the seasonal ratios, we have—

Table VII (a).2

Groups of stations.	Mean latitude of group.	Total years of record.	Percentage of annual rainfall.
	° ´		Spring.	Summer.	Autumn.	Winter.	Spring and Summer.
Eight stations in Dakota, Minnesota, and Nebraska	45 20	67	29	43	19	9	72
Three stations in Kansas	38 45	38	24	41	24	11	65
Eight stations in Texas	29 45	85	19	36	31	14	55

A moment’s inspection will show that the middle group is intermediate between the northern and southern in all its characters. The spring quota of rainfall progressively diminishes from north to south, and so does the summer, while the fall and winter quotas increase. What is lost in summer is gained in winter, and thereby the inequality of rainfall from season to season is diminished, so that a rainy season is not so well defined in Texas as in Dakota. What is lost in spring is gained in autumn, and thereby the place of the rainy season in the year is shifted. In Dakota the maximum of rain is earlier than in Texas, and corresponds more nearly with the maximum of temperature.

Table VIII.—Seasonal precipitation in the San Francisco Region.

Station.	Extent of record.	Mean annual rainfall.	Percentage of annual rainfall.
	Y. M.	Inches.	Spring.	Summer.	Autumn.	Winter.	Winter and spring.
Alcatraz Island	9 5	16.49	16	0	11	73	89
Angel Island	5 11	18.58	19	0	15	66	85
Benicia Barracks	18 3	14.90	28	1	15	56	84
Fort Miller	6 9	19.00	38	0	16	46	84
Fort Point	14 11	17.36	21	0	13	66	87
Monterey	12 3	15.71	28	2	14	56	84
Sacramento	18 3	19.24	29	1	14	56	85
San Francisco; Presidio	20 2	20.29	24	2	13	61	85
San Francisco	24 4	21.49	24	1	14	61	85
Weighted means	—	—	25	1	14	60	85

Total extent of record = 130 years.
Mean of yearly rainfalls = 15.90.

Second District.—In the San Francisco Region a rainy season is still more definitely marked, but occurs at a different time of year. It will be seen by Tables III and VIII that no rain falls in summer, while the winter months receive 60 per cent. of the annual precipitation, and the spring 25 per cent. The general yearly rainfall of the district is only about 16 inches, but by this remarkable concentration a period of five months is made to receive 13 inches. The winter temperature of the district is no less remarkable, and supplies the remaining condition essential to agriculture. Frosts are rare, and in the valleys all the precipitation has the form of rain. The nine stations which afford the rainfall records given above show a mean spring temperature of 57° (see Table IX). Thirteen inches of rain coming in a frostless winter and spring have been found sufficient for remunerative agriculture.

Table IX.—Mean temperatures, by seasons, for the San Francisco Region.

Station.	Extent of record.	Mean temperatures, in degrees Fahr.
	Y. M.	Spring.	Summer.	Autumn.	Winter.	Year.
Alcatraz Island	8 6	55	57	60	54	57
Angel Island	3 1	58	63	61	52	58
Benicia Barracks	15 7	58	67	62	49	59
Fort Miller	7 6	64	86	67	49	67
Fort Point	10 11	55	59	58	52	56
Monterey	12 5	55	60	57	50	55
Sacramento	14 0	59	71	62	48	60
San Francisco; Presidio	19 0	54	57	57	50	55
San Francisco	11 2	55	58	58	50	55
Means	—	57	64	60	50	58

The same winter maximum of rainfall is characteristic of the whole Pacific coast. The Region of the Lower Columbia, with an average rainfall of 46 inches, receives 47 per cent. of it in winter and 24 per cent. in spring. Southward on the coast, Drum Barracks (near Los Angeles) and San Diego receive more than half their rain in winter, but as the whole amount is only 9 inches agriculture is not benefited. The eastern bases of the Sierra Nevada and Cascade Range exhibit the winter maximum of rainfall, and this feature can be traced eastward in Idaho and Nevada, but in these districts it is accompanied by no amelioration of winter temperature. (See Table X.)

Table X.—Seasonal precipitation and temperatures on the Pacific coast, etc.

Station.	Mean annual rainfall.	Percentage of rainfall.				Mean temperature.
	Inches.	Spring.	Summer.	Autumn.	Winter.	Spring.	Winter.
San Francisco Region	15.90	25	1	14	60	57	50
Region of Lower Columbia	46.45	24	6	23	47	51	40
Drum Barracks, Cal	8.74	26	3	4	67	60	56
San Diego, Cal	9.31	20	4	20	56	60	54
Camp Independence, Cal	6.60	17	5	9	69	57	39
Fort Bidwell, Cal	20.23	24	8	15	53	48	32
Camp Warner, Oreg	14.41	30	8	17	45	42	29
Camp Harney, Oreg	8.76	26	13	18	43	47	27
Fort Colville, Wash	14.06	26	22	18	34	45	24
Fort Walla Walla, Wash	19.36	24	11	26	39	52	34
Camp McDermitt, Nev	8.53	35	9	13	43	46	29
Camp Halleck, Nev	10.98	33	11	21	35	45	28
Fort Lapwai, Idaho	14.89	28	16	23	33	53	33
Fort Boisé, Idaho	15.48	33	8	16	43	52	30

Third District.—In Arizona and New Mexico there is a general maximum of rainfall in summer, and a restricted maximum in winter. The principal minimum is in spring. In Table XI the stations are arranged according to longitudes, a disposition well suited to exhibit their relations. In eastern New Mexico the distribution of rainfall has the same character as in adjacent Texas, but with a more decided maximum. Half of the total rainfall is in summer and half of the remainder in autumn. Westward the maximum diminishes slightly, but it appears in every station of the two territories. In western Arizona the winter maximum of the Pacific coast asserts itself, and it can be traced eastward as far as Fort Wingate, New Mexico. Except at Camp Mohave, on the western border of Arizona, it is inferior in amount to the summer maximum.

Table XI.—Seasonal precipitation in Arizona and New Mexico.

Station.	Longitude.	Mean annual rainfall.	Percentage of annual rainfall.
	° ´	Inches.	Spring.	Summer.	Autumn.	Winter.
Western Texas	—	—	19	36	31	14
Fort Union, N. Mex	104 57	19.15	11	62	20	7
Cantonment Burgwin, N. Mex	105 30	8.65	18	34	28	20
Fort Stanton, N. Mex	105 38	20.94	14	51	23	12
Santa Fé, N. Mex	106 02	14.91	14	46	23	17
Albuquerque, N. Mex	106 38	8.11	10	54	25	11
Fort Fillmore, N. Mex	106 42	8.42	5	50	36	9
Fort Selden, N. Mex	106 55	8.49	7	57	22	14
Fort Craig, N. Mex	107 00	11.06	6	53	31	10
Fort McRae, N. Mex	107 03	11.59	21	53	20	6
Fort Wingate, N. Mex	107 45	17.32	11	38	20	31
Fort Bayard, N. Mex	108 30	14.32	11	50	16	23
Fort Defiance, Ariz	109 10	14.21	14	42	26	18
Camp Bowie, Ariz	109 30	15.26	9	48	13	30
Camp Grant, Ariz	110 40	15.08	14	41	22	23
Camp McDowell, Ariz	111 36	11.45	10	42	15	33
Camp Verde, Ariz	111 54	10.85	12	43	22	23
Camp Whipple, Ariz	112 20	19.28	20	42	11	27
Camp Mohave, Ariz	114 36	4.65	18	27	20	35
San Francisco Region	—	—	25	1	14	60

In all this region the daily range of temperature is great, and frosts occur so early in autumn that no use can be made of the autumnal rainfall. The yearly precipitation is very small, and the summer quota rarely exceeds seven or eight inches. Nevertheless the Pueblo Indians have succeeded, in a few localities, and by a unique method, in raising maize without irrigation. The yield is too meagre to tempt the white man to follow their example, and for his use the region is agricultural only where it can be watered artificially.

Notes

2 In computing the several means of Table VII (a) from the seasonal means of Table VII, the latter were weighted according to the lengths of the records by which they had been obtained.