Natural distribution map for <i>Crataegus douglasii</i> with the extreme northwestern, eastern, and southern populations circled in red
William B. Critchfield &amp; Elbert L. Little, Jr., U.S. Department of Agriculture &amp; Forest Service
1976
<a rel="nofollow" class="external text" href="https://esp.cr.usgs.gov/data/little/">USGS Geosciences and Environmental Change Science Center: Digital Representations of Tree Species Range Maps from "Geographic Distribution of the Pines of the World" by William B. Critchfield and Elbert L. Little, Jr.; Miscellaneous Publication 991, U.S. Department of Agriculture &amp; Forest Service, Washington D.C., February, 1966</a>