In Utah, Nevada, and other more or less arid parts of the western United States the steeper slopes of most of the mountains are fringed with alluvial deposits, which form bajadas, or alluvial slopes. The unit of a series of such deposits is the alluvial fan, the apex of which is in the mouth of a mountain canyon.

The surfaces and the eroded sections of these fans show two features by which they can be distinguished from the alluvial deposits of moister regions: many of the fans are strewn with large, isolated boulders, and the deposit as a whole consists of beds of unassorted and unstratified earthy material, a heterogeneous mixture of particles of all sizes, which in that respect resembles glacial till and some volcanic agglomerates. Lawson2 has given it the convenient name “fanglomerate.”

These deposits have generally been supposed to be formed by floods, although floods normally . . .

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