Information copied from Washington State Parks site, November 18, 2020 and subject to change.
Horses and riders are welcome on most ocean beaches and on established trails in 10 parks. At Bridle Trails, located at the edge of metropolitan Seattle, horses have the right of way on 28 miles of trails. Battle Ground Lake has a primitive horse camping area and five miles of riding trails, while Steamboat Rock offers 10 miles of trails in a classic Central Washington landscape of sagebrush and bare basalt cliffs.
This paved trail wanders for 37 miles alongside the Spokane River from Nine Mile Falls, just outside Spokane, all the way to the state line. (If you would like, you can keep on going right into Idaho.) Several significant historic sites are marked along the way, with many more signs still to come. The Spokane River Centennial State Park Trail is open to hikers, joggers, bikers, and in-line skaters. Certain portions of the trail are open to horses as well.
The Columbia Plateau Trail travels 130 miles from East Pasco to Fish Lake (near Spokane), through the channeled scablands and pine forests of eastern Washington. Only certain sections of these trails are currently paved or graveled. Future phased-development plans call for additional surface improvements and the addition of primitive campsites.
The Klickitat Trail runs 31 miles through stunning Columbia River Gorge country between Lyle and the Goldendale plateau. As it leaves the Columbia to follow the Klickitat River, the gentle trail leads cyclists, hikers, birders and, in some places, equestrians through dramatic Swale Canyon.
The Palouse to Cascades Trail follows the former roadbed of the Chicago-Milwaukee-St. Paul-Pacific Railroad two-thirds of the way across Washington, from the western slopes of the Cascade Mountains to the border with Idaho. The 100-mile portion from Cedar Falls (near North Bend) to the Columbia River near Vantage is open to hikers, bikers, equestrians, and horse-drawn wagons in summer, and to snowmobiles, dog sleds, and cross-country skiers in winter.
Willapa Hills State Park Trail is a 57-mile-long rail-to-trail, running east-west between the cities of Chehalis in Lewis County and South Bend in Pacific County. The trail is a key segment of Washington State Parks' plans for a cross-state trail network running from the Idaho Border to Willapa Bay, where it intersects Highway 101 near the Pacific Coast.