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I I, . i I I i SOME FLOODS IN THE ROCKY MOUNTAIN REGION. .107 rains, which are locally termed cloudbursts, and the east side of the Arkansas Valley between Granite and Buena Vista, embracing the western slope of the Park Range, is also subject to occasional cloud- bursts, which, however, are not so severe as those in the foothill region. Cloudbursts have also been recorded near the mouth of Texas Creek above the Royal Gorge and on Williams Fork near Hot Sulphur Springs, in Middle Park. - The eastern slope of the Big Horn Mountains is subject to cloud- bursts, but it is impossible to determine the other areas in Wyoming where they occur most frequently, as very f_ records of cloud- burstsUare available for Wyoming. Most cloudbursts occur at altitudes between 6,000 and '7,000 feet, althougjl those near Ouray are between 8,000 and 9,000 feet, those near Granite about 9,500 feet, and the one series of cloudbursts recorded on North Fork of Shoshone River in northern Wyoming at 10,000 feet, Cloudbursts occur only where there is a marked range in temperature within a relatively small area.. This condition exists chiefly in the foothills, where the warm air from the plains drifts toward the mountains, is deflected upward, and rapidly cools at the higher altitudes near the heads of the canyons. For this reason, cloudbursts generally occur in the afternoon or early evening of an unusually warm day, It is readily seen that they can seldom occur at higher altitudes in the mountains, as there the differences in temperature are usually insufficient and the mass of warm air in the high valleys is not great enough to cause any decided drift toward the adjacent mountains. The cloudbursts on North Fork of Shoshone River, which occurred at an altitude that is generally considered above the limit for cloud- bursts, . followed several days of unusually warm weather (p, 114) during which the air in the valleys became so much warmer than . the air at higher altitudes as to drift toward the mountain sides, where it was rapidly deflected upward. . - INTENSITY OF RAINFa=, The Weather Bureau maintains regular stations at Denver, Pueblo, and Grand Junction, Colo., and at Cheyenne, Sheridan, and Lander, Wyo., where continuous rainfall records are kept. - The stations at Denver, Pueblo, Cheyenne, and Sheridan are on the plains, a short distance east ~f the mountains, in the zone subj ect to cloud- bursts; and the rainfalls of greatest intensity recorded at these stations are given in the following table. Grand Junction is in western Colorado, in the region of flat-topped mesas, and Lander is in the rilOuntainous area of central Wyoming. At neither Grand Junction nor Lander has the intensity of rainfall been sufficient to be termed excessive. .