Description
During a phase of Plio-Pleistocene deformation in the Panache Hills region of Fresno County, California, Upper Cretaceous rocks of the Great Valley sequence were deformed into a broadly folded dome. Fractures within the Moreno Shale were filled with sand from one of that formation's lower members, the Dosados Sandstone and Shale Member. Some of the sandstone dikes and sills are nearly one-half mile in length. Most of the intrusions mapped were one to two feet in width, but dikes six to fifteen feet wide were not uncommon, and one dike was over twenty-three wide. A contoured Lambert-equal area plot of poles to dike and sill planes established the existence of three dominant joint planes or sets: (1) a primary dike set, striking N58°E and vertical; (2) a secondary dike set striking N8°W and also vertical; and (3) a secondary joint set representing sills striking N27°W and dipping 44°E. Comparing the orientation of the dike sets with diagrams drawn by Badgley (1959) suggests the possibility that the dike sets represent infillings of second order shear fractures. It is the opinion of the writer that the sills represent sand intrusion along flexural-slip joints.
