The northwest-trending San Andreas is the principal right-lateral fault of the region, and there are probably a dozen important others. The Big Pine-Garlock northeast-trending fault is the principal left-lateral fault of the region, and there are probably a half dozen important others.

An accumulation of many miles of strike-slip on these faults is likely. The juxtaposition of dissimilar rock sections may be explained by such movements. If so, the generally accepted histories of vertical displacement are doubtful, as are numerous interpretive geologic maps.

These faults comprise strain systems of north-south shortening. Northeast-southwest counterclockwise compression, perhaps due to subcrustal flowage from the Pacific, may be responsible for the lateral faults and other structures of the region.

Much more work is required before the ages and displacements of the lateral faults can be determined. Such work necessitates approaches which are now seldom used. Until this is at least partly accomplished there is apt to remain a critical hiatus in our knowledge of the geologic history of California.

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