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Why are basins in the Basin and Range Province often filled with sediment?

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tectonic basins and rift valleys Escarpments of the Great Rift Valley rising above the plain north of Samburu Game Preserve, central Kenya. Beisa oryxes graze in the foreground.

Basins in the Basin and Range Province are frequently filled with sediment due to the region's specific erosional-depositional system. The province is characterized by numerous mountain ranges separated by adjacent basins, a configuration created by normal faulting that uplifted mountain blocks and dropped basin floors.

Over geologic time, the mountains are slowly worn away by erosion. Drainage systems, often driven by seasonal rainfall or rapid snowmelt, transport the resulting debris from the mountain canyons into the adjacent basins. This sediment accumulates at the base of the mountains in the form of alluvial fans, which serve as the primary sites of deposition. Because many of these basins lack outlets for their drainage, the sediment remains trapped within the system, gradually filling the basins and burying the lower portions of the mountain ranges.12