CLIMATE BETWEEN FORT FILLMORE AND THE CORDILLERAS. 
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The two first may be looked on as one valley. The two last have the lower mountain lime¬ 
stone and the Devonian sandstone conglomerates resting on primary rock. In these valleys 
the geological circumstances are eminently favorable for artesian boring, and there water might 
be had at 300, 500, or 600 feet deep, according to the distance selected from the margin of the 
basin, provided the climatal conditions were favorable ; east of these basins the country is too 
much broken up by faults and dislocations to he available for ordinary artesian wells. 
2. The meteorological conditions may be thus expressed : 
The region lying between 30° and 33° north latitude is one of summer rains ; within 100 
miles of the Cordilleras it is a rainless district; but along parallel 32°, when it does rain, it is 
only in summer. This, of course, applies only to the country between the Sierra Nevada and 
the Rio G-rande, for in west Texas, under this parallel, it is a district of autumn rains, and 
between the Sierra Nevada and the coast it is a region of winter rains. 
The elevation of the district is as follows : 
Fort Fillmore, on the Rio Grande, altitude. 4,000 feet. 
Basaltic belt and porphyritic district, average for 105 miles.. 5,000 feet. 
Small basin district, 130 miles. 4,000 to 3,000 feet. 
From the last level, 3,000 feet on the San Pedro, the land falls until the junction of the Gila 
and Colorado is reached, when it is only 105 feet above sea level. 
The elevation of the mountain tops are : 
Summits of the Organ mountains. 7,000 feet. 
Chiricahui, or Mount Graham range. . 6,800 feet. 
Sien’a Nevada, on parallel 32°. 6,500 feet. 
In the two first instances the mountain tops do not exceed 2,000 feet above the plain, and, 
therefore, constitute but small points of attraction to rain clouds. The Sierra Nevada, on the 
other hand, is elevated nearly 6,000 feet over the district, immediately to its east, and hence 
becomes an impassable barrier. 
The annual fall of rain over the district is thus distributed : 
Annual fall at Fort Yuma under. 3.00 inches. 
Annual fall at Fort Fillmore, mean of three years. 9.23 inches. 
Annual fall at Fort Bliss, mean of three years. 11.21 inches. 
Forts Yuma and Fillmore are the extremes of the line. Fort Bliss is inserted to show the 
difference which a position 40 miles further south produces. The rain is accompanied by 
south winds, generally from the southeast or along the course of the Rio Bravo, but occasion¬ 
ally from the southwest. From the Rio Bravo the rain fall diminishes toward the west, until 
it is almost nothing upon the Colorado desert. 
The rains at San Diego have no relation with those at Fort Yuma, although both places be 
in the same latitude, and only 220 miles apart, the mountain chain of the Cordilleras altering 
the climate of the two stations. 
The cause of the diminution of the rain westerly may be due to two causes: 1st. That as the 
rain clouds come from the east, in passing over the district, they gradually become drier; and 
2d. As the district west of the San Pedro gradually drops toward the Pacific, and thus becomes 
more heated by the sun’s rays, the rain clouds are not condensed, but are raised further up in 
the atmosphere by the heat of the lower regions. In the Colorado basin clouds from the south 
were frequently seen drifting north, and when nearly overhead, gradually breaking up, and 
being dissipated under the immense heat of the plain. The difference in amount of rain fall 
