I finally discovered the shortcut to the Grand Canyon Trailhead. The official route to the trail involves walking a 10 mile round trip along the West Side Rd (not worth it). The short cut is only about a 1/2 mile round trip. Drive Tiger Mtn Rd SE about 2 miles from it's northwest entrance from Issaquah Hobart Rd. The trail is on the left about 200ft before reaching 260th Ave SE. The trail is marked by 2 steel utility plates and a bogus ""No Trespassing"" sign. The map clearly shows that this is DNR public property. The neighbors in this area have obviously bullied DNR into not advertising public access here. You are not allowed to park on Tiger Mtn SE so I legally parked on 258th about 100 yards away. The well worn trail traverses forest and intersects the West Side Rd in 1/8 mile. Turn left and in 1/8 mi you'll see the 15 mile creek trailhead on the right. There is a parking lot, interpretive signs and a fancy bathroom at the trailhead. Unfortunately it gets almost no use since the West Side Rd was closed to the general public a few years ago. The trail starts out as a gravel path. At a Y in the trail at .4 mi the left fork goes a short muddy distance to a small waterfall. This marks the entrance to the slot canyon exaggeratedly refered to as the Grand Canyon. A right at the Y leads up the canyon another .5 brushy miles to the trails end. All in all it is an easy, pleasant riparian trek. Calling it a ""Grand Canyon"" is a bit grandiose.

My daugther and I did a long hike on road and trail to see the wonders of the Grand Canyon of 15 mile creek. The falls and creek canyon are beautiful and the day was excellent. The weather was warm and the road and trail travel fast. The 15 mile creek canyon is worth seeing, but I am not sure its worth the 10 miles of road walking we did to get to the trailhead. This hike is good for conditioning as the road is in good shape and the trail is interesting if very short. We were passed by two groups of vehicles walking on the road, both groups were at the trail head. Question, how did they get by the gate and what is needed to get a gate pass? The Grand Canyon of 15 mile creek would be a great young family hike if there was a way of getting past the gate at the Tiger Mt. Summit Trail Head on Highway 18.