During September 5-7, 1970, unusually large floods occurred in the mountains of central Arizona and in the Four Corners area of Arizona, Utah, Colorado, and New Mexico. Flooding also occurred in southern and northeastern Arizona. The record-high rainfall of September 5 occurred when a mass of moist tropical air from Pacific storm Norma collided with a cold front from the northwest. A new 24-hour precipitation record of 11.40 inches (290 millimeters) was established for Arizona, and new 12- and 24-hour precipitation records of 6.0 inches (152 millimeters) were established for Utah.
The flood took the lives of 23 persons and was reported to have caused about $8.4 million in damage in Arizona. The main area of flooding was in the mountains in central Arizona. The flood generally was less destructive with increasing distance downstream; in the Salt and Verde River basins the reservoirs were capable of storing all the floodwater.
Flooding in the Dolores and San Juan River basins in the Four Corners area was mostly in rural areas, and two people were drowned in McElmo Creek in Utah. The flood was not as large as that of October 1911, which is the largest known flood in the area. A second storm occurred in the Four Corners area September 12-14; however, the amount of flooding generally was less than that from the previous storm. Flood damage as a result of the two storms was reported to be about $2.9 million.
