Just went on a hike. You could look for some alpine flowers and grow them in the cracks. There were some pretty awesome ones at the botanic gardens. I saw trees growing out of crazy small notches or cracks on the hike. There is also some kind of light green plant that seemed to grow on anything. The rocks look like they have a moss/lichen look already but you could test painting some moss on a section and see if you could get it to “patina” a bit more? Or what about succulents in some kind of pots or a little crack/area/something that follows the slope? They need very little to grow as well.

The botanic garden on York has a whole section that shows growing alpine plants in crevices.

Sorry I somehow didn't see this posted earlier. Wow, what an unusual and cool "rock feature" to have! It's unique in that it seems to be very nearly ALL rock, which could really make for some interesting arrangements in those cracks.

Alyssa mentioned some great ideas. You could additionally contact the folks over at the Rocky Mountain chapter of the North American Rock Garden Society (NARGS). What altitude you're at, what direction the yard faces, and surrounding structures (think microclimates) could make a big difference in what plants would do well.

Best wishes,

L