Northwest of Spokane, the 10,000 acre Riverside State Park has 40 miles of bridle trails. Plus, there is a concession for horse rentals and guided tours.
To reach Riverside from Spokane on US90, use Exit 280. Cross the Maple Street bridge and then turn left at Maxwell. Follow Maxwell (it turns into Pettit) past the Downriver Golf Course to the park entrance.
Overall, Riverside State Park is the 14th most popular horse trail of all 32 horseback rides in Washington.