White Rock Larkspur (Delphinium leucophaeum) is only found in 20 sites in the northern Willamette Valley in Oregon, and one occurrence in Lewis County, Washington. Scientists have hypothesized that Delphinium leucophaeum evolved in the wake of the Pleistocene epoch floods of the Columbia River (a/k/a the Bretz Floods) that occurred between 12,800 and 15,000 years ago. The Bretz floods scoured the north end of the Willamette Valley and created a temporary lake that extended south to the present-day city of Eugene. The lake repeatedly filled and drained, creating massive habitat disturbance and laying new deposits of silt and gravel in the valley. New forms of Delphinium were likely produced through hybridization and/or mutation in these disturbed areas and evolved into our localized Willamette Valley larkspur endemic species. White rock larkspur appears to have derived from Delphinium nuttallii.