<P> In the Cretaceous , a subduction zone formed at the edge of the continent . This means that an oceanic plate started to dive beneath the North American plate . Magma formed through the subduction of the ancient Farallon Plate rose in plumes ( plutons ) deep underground , their combined mass forming what is called the Sierra Nevada batholith . These plutons formed at various times , from 115 Ma to 87 Ma . The earlier plutons formed in the western half of the Sierra , while the later plutons formed in the eastern half of the Sierra . By 66 Ma , the proto - Sierra Nevada had been worn down to a range of rolling low mountains , a few thousand feet high . </P>
<P> In the Cretaceous , a subduction zone formed at the edge of the continent . This means that an oceanic plate started to dive beneath the North American plate . Magma formed through the subduction of the ancient Farallon Plate rose in plumes ( plutons ) deep underground , their combined mass forming what is called the Sierra Nevada batholith . These plutons formed at various times , from 115 Ma to 87 Ma . The earlier plutons formed in the western half of the Sierra , while the later plutons formed in the eastern half of the Sierra . By 66 Ma , the proto - Sierra Nevada had been worn down to a range of rolling low mountains , a few thousand feet high . </P>
what plate is the sierra nevada mountains on
what plate is the sierra nevada mountains on
Farallon Plate
Farallon Plate