Magnetic susceptibility was measured on conglomerate clasts and associated matrix along with medium-grained sandstone beds of the Upper Cretaceous strata within Silverado Canyon, Santa Ana, California. A hand-held magnetic susceptibility meter was used on conglomerate clasts and sandstone beds of the Trabuco Formation, Baker Canyon Member and Mustang Spring Conglomerate Lens of the Ladd Formation, and the Schulz Ranch and Pleasants Sandstone members of the Williams Formation. The upper 10 meters of the Trabuco Formation are the starting point, and the lower constraint, of this study. Average magnetic susceptibility (AMS) was determined from counts of 100 clasts within the Trabuco Formation, Baker Canyon conglomerate, and Mustang Spring Conglomerate Lens. AMS was determined for medium-grained sandstone beds throughout the stratigraphic section. Where outcrops permitted, sandstone beds were measured at Jacob Staff intervals. Results of data are as follows: Trabuco Fm. has an AMS of 58 for clasts, and 19 for sandstone matrix. The Baker Canyon conglomerate has an AMS of 27 for clasts and 15 for sandstone matrix. The Baker Canyon sandstone beds have an AMS of 6. Clasts in a conglomerate lens within the Baker Canyon sandstone yield an AMS of 195 due to the high magnetic susceptibility of aphanitic volcanic clasts. Within this conglomeratic lens the sandstone matrix has an AMS of 30. The Mustang Spring Conglomerate Lens gives AMS readings of36 for clasts and 4 for sandstone matrix. AMS for the Schulz Ranch Sandstone Member is 0, and AMS for the Pleasants Sandstone Member is 8. Sandstone beds and sandstone matrix appear to closely follow patterns of magnetic susceptibility associated with the corresponding conglomerate clasts. Overall values of low magnetic susceptibility are consistent with readings of the currently exposed eastern side of the Peninsular Ranges Batholith.