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| The Willis Palms Grove is growing on the along a trace of the Banning Fault (branch of the San Andreas Fault). Springs form along the fault where porous alluvial gravels are juxtaposed to clay-rich basin sediments that act as a barrier to groundwater flow. Hydrostatic pressure produces a number of seeps and small springs and associated deposits amongst the grove. The steep slope along the face of the hillside is a fault scarp. The hill in the background is rising relative to the flats at the base of the hill. However the ratio of movement of the fault is probably more in the range of 10 feet horizontal right-lateral offset for every 10 feet of vertical offset -- with the west (downhill) side moving north relative to the east side of the fault. |
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