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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 system). Springs form along the fault where porous alluvial gravels are juxtaposed to clay-rich basin sediments (Imperial Formation; Powell, 1985) 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. Although overall, the San Andreas Fault system displays right-lateral (horizontal) displacement, there is some vertical component of movement in many places along the complex fault system. Here, the hill in the background is rising relative to the flats at the base of the hill. |
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