If slope known or suspected to be unstable engineering solution needed rather than plants, which will simply slip along with the soil.

I've used cotoneaster on a slope. It needs some pruning to keep it neat but not much. It stabilizes the slope nicely, the birds like the flowers, and the deer don't eat it! It will depend on the angle of the slope however. You may need to terrace the slope.

What direction does the slope face?
Are you talking about puget sound "water" (moderating climate), or a lake somewhere inland with harsher climate?

Slope is approximately 22% and is on the Puget Sound.

Slope is facing west.

Low, spreading groundcovers are best for this purpose. If stabilization is an issue, check with the DNR attempting any planting - they will have advice and specific plant recommendations. I did a design for a similarly sited property involved with slide remediation plantings and there were only parts of the slope that were approved for cultivated plantings or even access. For those that were, the plants used (DNR approved) were Lonicera pileata and Genista pilosa. Both are very slope friendly, evergreen, drought tolerant one established and grow and establish rapidly.