If you live in the greater Seattle area or anywhere close to Puget Sound, you are zone 8. Zone 7 is not until you are up in the Cascade foothills.

Woody groundcovers are the best for erosion control and these are never available by seed. A 75 degree slope is extremely steep and I would suggest using geotextiles to secure the slope before planting. Plants that could work for you are kinnikinnick (Arctostaphylos uva-ursi), bearberry (Cotoneaster dammeri), creeping raspberry (Rubus calycinoides), salal (Gaultheria shallon) and low Oregon grape (Mahonia repens). All will tolerate partial shade, all are evergreen and the kinnikinnick, salal and Oregon grape are native plants so minimal maintenance required once established.

Another excellent plant for slope stabilization that is not a groundcover is our native western sword fern, Polystichum munitum.