Parking at the Devil's Thumb Trailhead off CR 128, follow the signs towards Devil's Thumb. The first intersection you'll come to (shortly after the first big alpine field) will be the Continental Divide Trail (CTD). Take a left, and keep following the little markers for the CTD. The trail is very well worn, so this shouldn't be a problem. However, this is where the trail starts getting steep in sections and the rocks/roots make their appearance.
You'll continue on the CTD until you reach the Columbine Lake Trail, where you'll take a left and quickly come upon the Junco Lake Trailhead/Parking Lot. From here, you can continue down to Meadow Creek Reservoir, or turn around for a mostly downhill ride back!