From the shared trailhead with the New Caribou Lakes Trail, descend to the creek and keep an eye out for a tree on the left with a sign that simply says "Trail" with an arrow pointed across the creek. Cross the rocks and follow signs for "Caribou Lakes Trail." From there it is a rolling, singletrack trail with a lot of variety from pine forest to granite faces.
After several short switchbacks and two long ones, you'll come to a split off for "Caribou Lakes Old Trail" on the left. Follow this trail for a very steep climb up to a beautiful pass with gorgeous 360-degree views including Mt. Shasta in the distance. The trail then dives down steep grades until it meets back up with the New Trail. Take a left after the trails join to the Lower Caribou Lake before a quick climb to the finish at Upper Caribou Lake. There are plenty of primitive campsites at both Upper and Lower Caribou with beautifully clear waters to refresh you.