The San Andreas system begins
The Farallon plate is consumed until the Pacific plate touches North America, and the margin starts sliding instead of subducting.
- When
- —
- Duration
- 5 million years
- Known to
- ± 2 million years
- Era
- Oligocene, Cenozoic
Around 28 million years ago the last of the Farallon plate between the Pacific plate and North America is subducted, and the Pacific and North American plates come into direct contact. Because their relative motion is nearly parallel to the margin, the boundary converts from subduction to strike-slip, and the San Andreas fault system is born, lengthening in both directions as the triple junctions migrate. It is the reason California has earthquakes rather than a volcanic arc along most of its coast.