It was hard, rough work, and risky because it could not be accomplished slowly.

Brush and rocks, loose shale and weathered slope, long, dusty inclines of yellow earth, and jumbles of stone--these made bad going for miles of slow, zigzag trail down out of the cedars.

Then the trail entered what appeared to be a ravine.
That ravine became a canyon.

At its head it was a dry wash, full of gravel and rocks.

It began to cut deep into the bowels of the earth.