The park originated in 1950, when Washington State Parks purchased a 160-acre parcel from Puget Sound Power and Light. Originally named Twin Falls State Park, following the park's expansion in 1976 its name was changed to Olallie, after a Chinook word for the berries which are common in the park.[2]
Features
The park features old-growth forests and five notable waterfalls: Twin Falls, Middle Twin Falls, Upper Twin Falls, Weeks Falls, and Upper Weeks Falls.
Twin Falls features a well-hidden underground run-of-the-river hydroelectric project that generates 24 MW of electricity.[5] The powerhouse is located 325 feet (99 m) below ground.
Upper Twin Falls
Middle Twin Falls
Lower Fall of Twin Falls
Upper Weeks Falls
Weeks Falls
Activities and amenities
Park activities include fishing, hiking, mountain biking, bird watching, and rock climbing.[2] Completed in 2017, the Ollalie Trail added 9.2 miles (14.8 km) of backcountry mountain biking.[6]