Impenetrable

You’re looking at the eastward exit from Zion National Park. The tunnel through this otherwise impenetrable wall begins just out of frame to the right, a couple switchbacks up the canyon. If you look closely at the shaded canyon wall to the top right of frame, you’ll find one of several openings which admit light into the tunnel the highway passes through. (That’ll be easier using this full-size photo.)

So, the canyon is already penetrated. Which is an intentional irony for the poem. 😉