Q.We need a privacy hedge or trees in our yard. We have extremely rocky soil in Washington state near Yelm.
Full sun is not a problem in the location we need them.

Certified GKH Gardening Expert
Many possibilities, here are a couple of links that may help you decide, based on the height requirement and irrigation. As long as there is drainage so water does not sit and rot the roots, rocky soil can be improved with soil analysis and prescription mineral and biological amendments. Or you can start with do it yourself composting and organic fertilization.
You are in zone 8, so here are some suggestions. You can also visit local arboretums and nurseries for ideas.
https://www.gardeningknowhow.com/ornamental/shrubs/shgen/gravel-garden-shrubs.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/working-in-rocky-soil.htm
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-8/zone-8-hedges.htm
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-8/zone-8-evergreen-shrubs.htm