This weekend I had a great trip with a couple friends to bike to the Tenino quarry pool from the Chambers Lake Trailhead. The ride is smooth paved trail most of the way, with only a quick road and gravel sections.
Directions: Take the Chehalis Western Trail from the Chambers Lake Trailhead (milepoint 7) and ride south 14 miles to the Yelm-Tenino trail. Head right (west) at the junction to Tenino. The quarry pool is well marked just past the field/fairground area.
Tenino quarry pool: $5 entry for non-locals
Photos from City of Tenino.