Then I came to the Grand Canyon of Yellowstone, a chasm cut by a river over several million years and still changing through erosion and tremors.
(I; came; to the Grand Canyon of Yellowstone; T:Then) (a chasm; cut; by a river; T:over several million years and still changing through erosion and tremors)
I a chasm
came cut
to the Grand Canyon of Yellowstone T:Then
by a river T:over several million years and still changing through erosion and tremors