Figure 27. Southeastern segment of the Whittier fault across Santa Ana Canyon. Interpretation of hanging-wall block of Santa Ana Mountain Boundary Fault (footwall block of Whittier fault) is based mainly on surface mapping of Durham and Yerkes (1964) and Schoellhamer et al. (1981) and wells not on section. Interpretation of hanging-wall block of Whittier fault below well depths is based on the thickness of the Cretaceous sequence in Prado Petroleum Government No. 165-1 well (Lang, 1978), located 3.3 km southeast of the section line, and the extrapolation of outcrop data from the Santa Ana Mountains. The base of the Lower Fernando Member is approximately located with unpublished microfaunal data (Aera Energy LLC) from Grayco Oil Grayco No. 1 well.