Highway 23 runs along mostly rugged terrain. In the north, it traverses Grimes Canyon, one of the more treacherous highways in Ventura County. It acts as a commuter link from the Santa Clara River Valley to Moorpark. Owing to the geology of the area, the roadway is subject to rock-slides in summer and mudslides in winter. Plans were made in the past to bypass the worst of the canyon by a freeway, but these never made it past the drawing board.
South of US 101, State 23 follows Decker Canyon Road. This road is quite narrow, a substandard width in fact, in many places from State 1 to near Mulholland Highway east. The center segment is a six lane freeway built mostly in the late 1960’s and early 1970’s.