That's in the Basin and Range province (most of Nevada is in this province).
It's a zone of crustal extension, with the crust being pulled apart on an east-west axis. This leads to the characteristic horst and graben geography, with valleys interspersed with mountains. It also means the crust has become thinner. This has brought hot rocks closer to the surface, where some have melted due to decompression, allowing magma to flow up through all those normal faults, creating volcanism.
It's a zone of crustal extension, with the crust being pulled apart on an east-west axis. This leads to the characteristic horst and graben geography, with valleys interspersed with mountains. It also means the crust has become thinner. This has brought hot rocks closer to the surface, where some have melted due to decompression, allowing magma to flow up through all those normal faults, creating volcanism.