West Bench starts near the Jumbo Lake reservoir/Mesa Lakes area of the Mesa. It's fairly easy to get to - park down by the lake. Ride up the paved road past the little ranger station and across the bridge to your left. There is a sign there that says "West Bench ski trail." (It's a cross-country ski trail in the winter.) From here follow the singletrack trail for about 1/2 mile. Then you'll hit a gravel/paved road and see cabins. The most obvious cabin is a red one close to where you meet the road. The trail continues just to the left of this cabin - between it and another one. There is a post there, but no sign.
The fun begins with a loose rocky downhill and several lava rock obstacle courses. These can be entertaining and challenging!
West Bench can be a great ride - but be prepared! Mosquitos can be out, bogs need to be traversed, and there may just be too many trees down for it to be a lot of fun once you get past the first Powderhorn cut-off. Still, it was a great day for an awesome bike ride; sitting by a quiet lake enjoying a beer afterwards didn't hurt either!