The northern half of the Lake Walcott 30 x 60 minute quadrangle shows the geology of the southern part of the Craters of the Moon lava field, the complex geologic features of the Holocene Kings Bowl and Wapi lava fields, and the southern part of the Great Rift volcanic rift zone. The long extent and distribution of skylights in lava-tube systems of the Horse Butte and Wapi Park lava fields are depicted on this map. 40Ar/39Ar and K/Ar age determinations give detail to the Holocene, late Pleistocene, and late middle Pleistocene volcanic for lava fields in this quadrangle. Most of the younger basalt eruptions (<150 ka) have occurred along the Great Rift volcanic rift zone, but two of the younger lava fields are located in the western part of the quadrangle. Kimama Butte, a shield volcano, is 87 +/- 11 ka and Shale Butte is dated at 11 +/- 6 ka. Paleomagnetic studies have shown that the Horse Butte-Inferno Chasm eruptive fissure system has at least 5 paleomagnetic-correlative lava fields, the Claasen vent complex consists of at least 7 correlative lava fields, and the Streifling-Flat Top vent complex includes at least 4 correlative lava fields.