Part of the field is the Begour crater. It is about wide and is mostly dry with the exception of several small ponds and a ring of diatom- and mollusc-containing sediments which forms a ring terrace inside the crater. Radiocarbon dating has yielded ages of 8,300 ± 300 years ago on sediments within Begour, and Tarso Toh is considered to be a Holocene volcano.