[Wikipedia] Range: Lupinus rivularis is found in western North America, from southern British Columbia to northern California.[2] Specifically, it is native to California, Oregon, Washington, and British Columbia.[2] It mainly exists from coastal habitat in places such as both Olympic and Redwood National Parks, and at Point Reyes National Seashore. (link added by Mary Ann Machi)

[explorer.natureserve.org] Hybridization with L. arboreus: This species hybridizes with L. arboreus, which is native in North America only to California, and non-native in Oregon, Washington and British Columbia. Genetic swamping due to hybridization is believed to be the greatest rangewide threat; it is uncertain how much "pure" L. rivularis remains, but it may be very little. (link added by Mary Ann Machi)