The Timer Mountain volcanic field, located approximately 150 kilometers northwest of Las Vegas, Nevada, consists mainly of basaltic cinder cones and lava flows. It has been active in 3 major cycles, starting 12 million years ago. The most recent eruptions probably occurred less than 10,000 years ago.
Timber Mountain's eruptive history consisted of 3 episodes: 12 to 8.5 million years ago, 9.0 to 6.5 million years ago, and 3.7 million to less than 10,000 years ago.
The older volcanic centers of the Timber Mountain volcanic field include small basaltic scoria cones and lava flows, mainly in the northeastern part of the field. Basaltic eruptions resumed at 3.7 million years, with a progressive decline in the volume. All basaltic centers of the latest period of activity were in the southwest part of the volcanic field.
There are 3 major centers of the younger activity in the Timber Mountain field:
1. Crater Flat
contains a series of deeply eroded, 3.7-million-year-old basalt scoria cones and lava flows in the eastern part. 4 more basaltic centers (1.2 million years old) are aligned along a NNE trending arc in the central area. The youngest center is the basalt of Lathrop Wells (100,000 to 10,000 years old) at the south end of Crater Flat.
2. Buckboard Mesa:
The basalt of Buckboard Mesa (2.8 million years old) erupted in the northeast part of Timber Mountain caldera.
3. Sleeping Butte:
2 other basalt centers (300,000 to 10,000 years old) are located 30 kilometers north of Beatty, Nevada, on the south flank of the Black Mountain caldera complex.
Buckboard and Sleeping Butte volcanic centers are within the controlled boundaries of the Nevada Test Site or the Nellis Bombing and Gunnary Range, and are not accessible to the public. The southern center of the Sleeping Butte group is visible from Highway 95, approximately 16 kilometers north of Beatty.
Source: CVO / USGS Nevada volcanoes information