Across the Columbia River from Vantage, Washington is an interesting roadside area (map) that is best described as a “natural rock garden”. I've centred the map in that link, and the extent of the area is roughly 2500m N-S x 1000m E-W (approx. 1.5mi x 0.5 mi).

Geologically, the area is composed of basaltic outcroppings with (curiously) some small sand dunes interspersed in low-lying areas. Basalt outcroppings are found throughout central and eastern Washington state, but in my experience (and from what I've heard from others), this particular area is special for the extent and diversity of associated vegetation. However, I don't know the area well enough to be able to say with certainty how this occurs (if I had to guess, I'd suggest higher rainfall).

The purple-flowered subshrub in the foreground is Salvia dorrii, or purple sage. Most of the yellow-flowered plants, I believe, are Erigeron linearis, commonly known as yellow desert daisy. I've not identified the other subshrub yet.