Geology of Canon de San Diego, southwestern Jemez Mountains, north-central New Mexico
— Shari A. Kelley, Robert G. Osburn, and Kirt A. Kempter

Cañon de San Diego (CdSD) provides an important window into the Proterozoic to Pleistocene geologic history of the Jemez Mountains region. Portions of oceanic shorelines and continental-scale river systems are preserved in the late Paleozoic to middle Mesozoic sedimentary rocks in the canyon. Recent mapping in the area has revealed the northern extent of an Oligocene to Miocene Rio Grande rift basin that developed against, and then overlapped, the Jemez fault zone. The older part of this basin, which is exposed on the hanging wall of the Jemez fault zone, is dominated by cobbles and boulders of Oligocene intermediate composition volcanic clasts from an unknown, but nearby, volcanic center. Offset on the Jemez fault zone decreases toward the northeast, and early rift displacement was taken up along a second NNE-striking fault, the Cat Mesa fault, located east of the Jemez fault zone in the eastern wall of CdSD. An apparent Pliocene (?) debris avalanche deposit composed of a basal debris flow deposit overlain by as much as 240 m of rubbly Paliza Canyon Formation andesite is exposed for 6.5 km along the western wall of CdSD; this unit controls the hydrology of the western side of the canyon. A river was present to the west of the modern CdSD prior to the eruption of the small volume 1.85 Ma San Diego Canyon tuff and that river system persisted until the eruption of the Otowi Member of the Bandelier Tuff at 1.61 Ma. Lake and fluvial deposits preserved 280 to 300 m above grade suggest that modern CdSD has had a protracted, episodic incision history.