A small group of volcanoes lies N of the town of Buta Ranquil, near where the Río Grande and Río Barrancas join to form the Río Colorado. Volcán Cochiquito is an alkaline basaltic stratovolcano with eight satellitic cones. Volcán Sillanegra (or Malal) is pyroclastic cone complex with two craters and basaltic aa lava flows located east of the Río Grande. Its age was estimated to be Holocene (González-Ferrán, 1995). Volcán Ranquil del Sur is a small stratovolcano south of the Río Barranca with an estimated Pleistocene-Holocene age that contains a 600-m-wide crater and produced andesitic pyroclastic material and lava flows. However, Folguera et al. (2006) describe Chochiquito as being erupted along a normally reactivated reverse fault in the Chos Malal belt, part of a group of basaltic domes and lava flows ranging from 3.2 to 1.5 Ma (citing dates in Linares and Gonzalez, 1987). Other researchers (e.g. Ramos and Folguera, 2011) map the area as older Pleistocene volcanics not part of the larger volcanic fields nearby.