Palouse Falls deep in a canyon carved through multiple layers of flood basalts.
John D'Onofrio did a write up on Palouse Falls in the Cascadia Weekly a_visit_to_palouse_falls. Palouse Falls is one of Washington State's true wonders. With the Cascade Range and the famous water falls of the Columbia River Gorge, Palouse Falls in the heart of one of the driest and hottest parts of the state is a remarkable outlier that is often forgotten. The waterfall alone is a wonder, but the setting and the story behind the landscape is a wonder as well.
The Palouse River flows from the moister and higher lands of Idaho and flows through the Palouse of Washington State. The Palouse is a large area of rolling hills constructed from a few million years of wind blown silt accumulations. The Palouse is a sea of wind swept wave-like hills with very deep, fertile soil. This soil overlays the Columbia River Basalts, one of the largest accumulations of basalts in the world.
Palouse with forest and prairie on steep slope between fields of winter wheat
Drier part of the Palouse showing hills constructed from wind blown silt
Massive silt typical of the Palouse area
The Palouse River previously flowed in a valley through the present day towns of Washtucna, Kahlotus and Connell and on to the Columbia River. However, during one of the great Missoula Floods, flood waters filled its entire valley with water spilling southward at numerous locations carving deep into fracture joints in the underlying bedrock of the Columbia River Basalts as the water headed towards the Snake River Canyon (Previous Post on Devils Canyon). At a bend in the Palouse Valley this erosion was deep enough into one of the joints that after the flood was over the Palouse River continued flowing down this overflow route within a deep narrow bedrock gorge and the former river valley was left nearly dry with the exception of a few seasonal ponds.
Google Earth image of lower Palouse River
Dashed blue lines bracket the Missoula Flood corridor
Dashed blue arrows show former river route
Former Palouse River valley near Kahlotus
As the Palouse River flows westward through the Palouse, it enters into an area of drier and drier climate. The area near Palouse Falls is one of the driest and hottest areas in the state with rainfall under 10 inches per year and very high summer temperatures that routinely pass 100 degrees. The river is in such a straight deep notch within the joint fracture, that unless you know the canyon is there it can not be seen until essentially reaching the canyon's shear edge. Note in the satellite image there are a number of other slots that were carved into the regional joint pattern which are now dry canyons. The uplands around the canyon have been stripped of soil from the Missoula Flood and the areas where the soil has not been stripped are just barely moist enough not to be active dune areas (there are active dunes a few miles to the southwest).
Road heading to Palouse Falls
This is a great time to visit the falls as the falls are in high water flow from snow melt in the mountains to the east. Jon D'Onofrio added a nice touch to his article, "We headed south out of the lonely hamlet of Washtucna through rolling hills that looked like a Lisa McShane painting and reached Palouse Falls State Park in the late afternoon". Indeed a number of Lisa's paintings are from that very area and she once lived in the now dry former Palouse River valley.