Assertion: alluvial fan's floor | /r/HasProperty | below baselevel
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Source sentences:
text: The floor of this depression being below baselevel, it has necessarily come to be the seat of the mountain waste brought down by the many streams from the newly uplifted Sierra Nevada on the east and the coast ranges on the west; each stream forms an alluvial fan of very gentle slope; the fans all become laterally confluent, and incline very gently forward to meet in a nearly level axial belt, where the trunk riversthe Sacramento from the north and the San Joaquin from the south-east--wander in braided courses; their tendency to aggradation having been increased in the last half century by the gravels from gold washing; their waters entering San Francisco Bay.