I'm looking for a cliff, detailed enough that a character could stand on top or at the bottom, and steep enough that falling would, uh, not be a good idea. Preferably with a desert look but I could re-texture it if necessary. Could have a flat top for a building/structure on top, or natural.

I'm seeing lots of things that look fine in the distance but not up close, or that aren't very steep, or are pretty small.

Any suggestions?

Have you looked at these Daz Store Arid Valley -

XI African Wildlands View Rock,  LI Elemental Dynamics - Rock Modules / Slabs 01, Little Desert Valley, Traveler's Naturals - Rocks Vol 6 - Cliff Rocks

Rocks Volume 4, Flat Rocks, DAZ Studio 4 Cliff Face Shaders, Stones HR, Magic Cliff, Rocky Desert for Simple Grassland Expanse, Rocks Volume 3

The Great Desert, AP Wild West Environment, Cliff Hanger, Modular Cliff Formations 2 and 3, Alter Rock for Daz Studio, Totally Stoned - Rock Monuments

Canyon Terrain

Some of the items above are for Poser but you can still use them in Daz Studio, just apply shaders.

Large rocks placed in the desert will give you the effect also.  Do many more just type desert in search box and also cliffs, and then rocks.

https://www.renderosity.com/marketplace/products/118675/3d-scenery-deepwood-gorge

I also like Danger Pass by Nerd 3D, but I can't find it on Rendo now.

Thanks, going through all those. I'm using Poser, so that's preferred although if something was really good DS isn't out of the question. (Although, oddly, Daz3D doesn't show DS-only products in my wishlist, I guess because of how I set the store filters.)

I am thinking I will probably need a big scenery prop for a wide shot and then stack up a bunch of small props for close-ups. Not really seeing anything that checks all the boxes at once.

Go to polyhaven.com and search for namaqualand cliffs. There are a few. Free assets, several formats.

These are nice cliff type rocks but a good starting base.