Island Rock is a prominent although obscure crag (deservedly so) on the south side of the creek. It faces northwest and so is usually shady. There are two old trad route, Cracks are for Kids, 5.8 and short, and the longer, decent-looking Lost Ring, 5.7, which I haven't done. Recently Vaino Kodas and Bob D'Antonio added the pretty good 11a sport climb No Man is an Island. There is room for more routes. The main face has a bunch of trad features, but it's pretty dirty. The (west-facing?) right face has some potential also, and there's another formation just up the hill.
4.2 miles up Boulder Canyon (Rossiter's mileages), about 0.3 miles past the Sugarloaf turnoff, there is an "island" of rock with a dirt road going part way around it on its left side, between the rock and the creek. Park here. Island Rock is the rock across the creek. Brick Wall is about 0.4 miles beyond Island Rock. The creek is often high, so much of the year the crag is hard to access. Cross the creek where you can and move left or right until below the crag. Continue up hill, and you will come upon an open grassy slope that leads to the base. Scramble up left towards a steep gully in rock to access Cracks are for Kids and No Man is an Island. Lost Ring is on the right prow of the main face.
Note, there is a fair amount of broken glass in this area, even going all the way up to the crag.
Mountain Project's determination of some of the classic, most popular, highest rated routes for Island Rock:
Difficult moves at every bolt. Cool slab climbing with great protection. At the third bolt...step left and down a little to a good pocket. Crank up on the pocket with little for the feet to some good edges, high step and clip the fourth bolt (crux). Reach another mantle at the fifth bolt, gain a ledge and the anchor. One of the better slab routes in the canyon. ...[more]Browse More Classics in CO
Presently the stream is just low enough to cross by rock-hopping. There is no trail per se, but it is still an easy 10 min approach to the base area for the left-3 routes. That thing over to the right has a terrible and dangerous approach though, up a very steep moss gully that would break your neck if you slipped.