Great quantities of dust are transported to central Arizona by strong summer winds blowing mainly from southern and eastern Arizona and northern Mexico. Dust collected periodically from April 22, 1972, to July 21, 1973, from the cedar shingle roof of a house in Tempe, Arizona, in the lower Sonoran Desert of the southwest United States, indicates a rate of deposition of 54 g · m²/yr, a rate equivalent to 5,400 t · ha/10,000 yr. Most of the dust is deposited in association with summertime dust storms (haboobs), which on the average occur 3.5 times per year in the...