These rocks were once part of a volcanic island chain that collided with western North America about 1.7 billion years ago.
(These rocks; were; T:once; part of a volcanic island chain) (a volcanic island chain; collided; with western North America; T:about 1.7 billion years ago)
These rocks a volcanic island chain
were collided
T:once part of a volcanic island chain
with western North America T:about 1.7 billion years ago