[Wikipedia] Limited Range: Polygonum bolanderi is endemic to northern California, where it is known from the northern Coast Ranges, the southern Cascades, and the northern Sierra Nevada (from Humboldt County and Shasta, south as far as Sonoma county and Tuolumne County). (link added by Mary Ann Machi)
Calflora:
Information on California plants for education, research and conservation,
with data contributed by
public and private institutions and individuals.
[web application]. 2025.The Calflora Database
[a non-profit organization].Available:
https://www.calflora.org/(Accessed: 03/28/2025).