In the Early Jurassic the Pacific Plate opened originating from a triple junction between the Panthalassic Farallon, Phoenix, and Izanagi plates.The [Pacific] plate first came into existence as a microplate 190 million years ago, at the triple junction between the Farallon, Phoenix, and Izanagi Plates.- West Coast of the United States (Wikipedia)
The West Coast of the United States – also known as the Pacific Coast, the Pacific Seaboard, and the Western Seaboard – is the coastline along which the Western United States meets the North Pacific Ocean. The term typically refers to the contiguous U.S. states of California, Oregon, and Washington, but sometimes includes Alaska and Hawaii, especially by the United States Census Bureau as a U.S. geographic division.
- Phoenix Plate (Wikipedia)
The Phoenix Plate (also known as the Aluk Plate or Drake Plate) was a tectonic plate that existed during the early Paleozoic through late Cenozoic time. It formed a triple junction with the Izanagi and Farallon plates in the Panthalassa Ocean as early as 410 million years ago, during which time the Phoenix Plate was subducting under eastern Gondwana.