Abstract

The northern portion of the northwest-southeast trending Great Valley of California is broken in the subsurface into several distinct tectonic subunits by a number of northeast-southwest trending basement faults, the largest being the Stockton (or French Camp) fault, with over 2000 feet of reverse or thrust fault displacement in the shallower upper Cretaceous stratigraphic section.

Similar features of lesser magnitude with the same geographic trend and exhibiting similar tectonic histories both to the north and south of the Stockton fault have been recognized by several explorationists and researchers but are less well documented.

While the smaller of these features appear to lose structural integrity to the west with thickening sedimentary cover and deepening Sierran basement, they exhibit several common characteristics and structural history which include: (1) two distinct periods of structural movement separated by a period of apparent non-movement; (2) involvement of Sierran basement, at least on the east side of the valley; (3) early indications of tensional or tranverse movement with significant growth on the downthrown side followed by a later period of apparent compressional movement; (4) reversal of apparent throw from the early movement to the late movement withthe initially downthrown hanging wall block exhibiting thrust displacement in the later compressional stage.

Between the two time periods of apparent movement seen on these faults, the dominant fault pattern in the Sacramento valley was related to the predominantly northwest-southeast trending Midland fault system with its large growth faults active from paleocene through early Eocene time.

It is suggested that these three periods of faulting correspond to an early period of regional plate convergence and subduction during the upper Cretaceous, an intermediate period of plate junction during the Paleocene and lower Eocene characterized by emplacement of diapiric ophiolite sequences such as Mt. Diablo near the outcrop of the Great Valley Thrust with the large growth faults of the Midland system being associated with these diapiric serpentinite emplacements; thirdly, a post-Eocene period of faulting wherein the dominance of strike-slip movement along the San Andreas fault system is associated with a change in regional stress which placed the previously tensional cross-valley faults into a compressional regional stress pattern and reactivated the older faults in a different structural setting.