Mossy tree branch pattern. Ravenna Park, Seattle, Washington, USA. Cowen and Ravenna Park were formed when melt-off from the Vashon Glacial Ice Sheet formed Lake Russell and cut drainage ravines through new glacial fill. Lake Russell disappeared when the Ice Sheet retreated north of the Straits of Juan de Fuca, but various features remained, including the Green Lake drainage basin, which continued to empty through the Ravenna ravine into Lake Washington. The deeper pockets of the basin became Bitter, Haller and Green Lakes. Many creeks and brooks and springs fed into Green Lake, whose outlet was on the east side of the route of Ravenna Boulevard, in a deepening ravine which became Cowen and Ravenna parks.