San Quintín volcanic field on the NW coast of Baja California consists of 11 late-Pleistocene to Holocene volcanic complexes. Low lava shields, initially submarine, are capped by well-preserved scoria cones. San Quintín rocks are similar to intraplate or oceanic island alkalic rocks and differ from other Baja alkalic volcanic suites. San Quintín is the only Quaternary volcanic field in Baja California where lower-crustal and upper-mantle xenoliths are found. The field is located at the margins of the Y-shaped San Quintín Bay and includes a northern and southern group of cones, Monte Mazo (connected to the mainland by a long tombolo), and Isla San Martín, 5 km offshore to the west. The youngest craters overlie deposits thought to be dated at 5-6000 years before present, and Gastil et al. (1975) considered the southern cones of Vizcaino and Sudoeste to possibly be less than 3000 years old. However, later Argon/Argon dating (Ortega-Rivera et al., 2004) restricted eruptions to a range of between about 20,000 to 180,000 years ago.