Although the San Diego maar has been known and described by Servicio Geologico Colombiana, along with dating by Toro (1988) that placed the most recent activity in the late Pleistocene-early Holocene, work by Borrero et al. (2016) provides a more comprehensive understanding of this volcano. The NNE-elongated crater is about 1.5 x 2.1 km and contains a lake about 230 m below the crater rim. A cone feature located immediately NE of the maar is the remains of a dacitic dome with landslides on the flanks. They determined that the volcanic features were all the result of a single monogenetic eruptive period that began with the vent opening and incremental growth of the original crater, followed by additional widening of the maar. Effusion of the dome was the last stage of active volcanism. A paleosol below the young maar sequence was 14C dated at 20,056 ± 93 years cal BP, and the dome was slightly younger at 18 ka BP based on fission track dating of apatite.