West of Cascades, S. Brit. Columbia to N. California.
"Pacific rhododendron is one of the shrubs eaten by mountain beaver in the Coast Range...
Pacific rhododendron may provide good thermal and hiding cover for big game animals. However, thickets can be difficult for the animals to enter. Presumably, Pacific rhododendron provides cover for smaller animals also." 
"Pacific rhododendron is the state flower of Washington. Kitsap Peninsula residents host an annual weeklong Rhododendron Festival during spring bloom. Pacific rhododendron is not as widely cultivated as the showier Rhododendron hybrids, but it is used as an ornamental in backgrounds or native gardens and naturalized woodlands. Native plants like Pacific rhododendron have potential value for low-water-use landscaping. Both white and pink forms are commercially available . Growing Pacific rhododendron in partial shade to full sun and debudding or pruning encourage compact growth and bloom. Wild plants are legally protected from digging." 
"Common rhododendron (Rhododendron ponticum), a closely related species, is poisonous to sheep. Pacific rhododendron may also be poisonous to sheep...
Pacific rhododendron offers erosion protection on steep watersheds." 
 Crane, M. F. 1990. Rhododendron macrophyllum. In: Fire Effects Information System,. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/plants/shrub/rhomac/all.html.