A pass is a low spot in a ridge, or divide, between two streams. As the glacier dam creating glacial Lake Watts began to retreat to the northwest (towards the viewer), Alpha Pass was uncovered, allowing Lake Watts to partially drain through this low spot between Bear Run and Slippery Rock Creek. Drainage was through this small valley toward what it now Alpha Falls, in McConnells Mill State Park. Drainage was from left to right in this view (east to west). Drainage through here lowered the level of Lake Watts approximately 20 feet. The valley has been greatly modified by Vanport Limestone mining.
Alpha Pass and valley are on private property. The photograph is from their north side along US 19.