Climate

ORGAN PIPE CACTUS NATIONAL MONUMENT lies at the eastern edge of the driest section of the United States and in the general area of highest temperatures. Daytime temperatures from December through February are usually in the sixties—what the local people call "shirt-sleeve weather." The air becomes warmer in March and April. From May until about October, maximum daytime temperatures usually exceed 100° F. The latter part of October and all of November are cooler. You can count on a drop of 30° between the high day and low night temperatures the year round. You need not be frightened away by those hot summer days, because, owing to the low humidity, you should find them much less unpleasant than you would similar temperatures in a humid climate. Autumn, winter, and early spring are, of course, more comfortable than summer.

Rainfall comes during December, January, and February, and in the July-September period. Winter precipitation consists of light, but steady, general rains that occasionally last for several days. Summer rains come in the form of sudden, brief, spotty, and often violent thundershowers, sometimes so torrential that they cause sheet floods and powerful, but short-lived, accumulations of runoff water rushing along desert washes.

Whether the maximum precipitation occurs in winter or summer, neither season can be depended upon to bring much moisture in any one year. One season may bring considerably more rain than the next several seasons, and in summer, parts of the area may be partially or entirely skipped while nearby locations receive a heavy downpour.

Visible evidence of this unequal distribution of moisture is presented by the condition of plant growth, particularly in the abundance and luxuriance of the spring flower display, which is acutely dependent upon winter rainfall. In Papagueria (land of the Papago Indians, of which Organ Pipe Cactus National Monument is a part), storms of freshet-making proportions may be 3 to 5 years apart, and the torrents instrumental in large-scale erosion are apparently separated by decades or even centuries. Because of the region's high temperature level, relative humidity is low, especially during the day, and evaporation of such moisture as may be present occurs at a high rate.

Winter rains create streams that may flow weakly in otherwise dry watercourses for a few days. Sudden local flash floods can cover parts of the desert with moving sheets of water and roar down arroyos for a few hours following violent cloudbursts. But there is almost no permanent surface water in all the 330,000 acres of the monument. In the mountains, there are a number of natural rock pockets, or tinajas, which collect and hold rainwater. These, together with occasional springs and seeps, provide the only natural water for deer, bighorn, and other animals that require moisture in addition to that which they obtain from their food.

Of the known dependable moisture sources, Dripping Springs, on the north side of the Puerto Blanco Mountains, and Bull Pasture Spring, about 20 miles north of the international boundary on the west slope of the Ajo Mountains, are small but important watering places for animals. Trickles from a series of warm (80° F.), mineralized outflows, totaling 43 gallons per minute at Quitobaquito Springs near the southwest corner of the monument, were united and impounded about 60 years ago with the aid of a series of low dikes. This formed a pond, which was used for primitive irrigation farming. Another water source, Rincon Spring, is about 1-1/2 miles northwest of Quitobaquito. There is a small spring, called Aguajita, half a mile east of Quitobaquito.