The Diversion of Irrigating Water From Arizona Streams

Most of the irrigating water obtained from Arizona streams comes from the higher mountains. Very little rain falls in the lower and more level country,.where cultivation is practicable. For ages the typical stream has gathered its load of silt, sand, and gravel in these mountains and forced it, by reason of strong slopes, through the canyons and down to the low country, where grades become less, and it is spread out evenly in the broad, gently sloping, cultivable valleys. Usually, such valleys show evidences of having been flowed by slack water for periods long enough to deposit deep surface beds of fine silt. The overflow has eventually cut its way out through surrounding hills, and worn down the outlet below the valley level.