The middle peak of the "Issaquah Alps" has horse trails leading from its south parking lot. The rest of the trails are hiker-only, so pay attention to the signs. The trails here are steep but lovely, so make sure your horse is in decent condition, and take your time to enjoy the woods.
The equestrian trail makes a large loop up and back down the side of the mountain, bisected lengthwise by a maintenance road that is also horse-friendly. This allows you to pick various lengths of ride depending on how you and your horse feel after that first big ascent. Ride a short trail from the parking lot to the gravel Squak Mt Road SE and turn right on the road.
From Issaquah, drive south on either Front Street/Issaquah-Hobart Road or on St. Rte. 900 to May Valley Road. From Iss-Hobart Road, turn right onto May Valley and drive 1.5 miles; the park entrance will be on your right. From SR 900 turn left onto May Valley Road and drive 2.5 miles; the park entrance will be on your left.
Length: ~7 miles
Surface: dirt, gravel road
Share with: hikers, bicycles (on road)
Restrooms, picnic tables
Parking for: 4-5 horse trailers,
depending on how many other vehicles are there & how they park. Loop
WA State Park:
This one from the website above, or also the trails are on the Green Trails Issaquah Alps map #203S.