2018 Map of Castle Rock Ridge

Tracing the northwestern to southeastern diagonal is the San Andreas Fault, a defining structural feature that cuts through Lyndon Canyon and near the Lake Ranch Reservoir. This fault line separates the drainage systems that feed into the San Lorenzo River to the south and Saratoga Cr to the north. The presence of numerous named gulches like Hopkins Gulch and Harmon Gulch highlights the deeply dissected nature of the terrain west of the divide near Bear Creek Summit.