Take Forest Road 365 from Pettit Lake for about 1.5 miles. It will curve around to the north through some sagebrush. Near the end of that look for a fork just before it heads west back into the trees. Look for the sign to Yellowbelly Trail and a small parking area, this is where the trail starts.
From here it is just over a mile to Yellow Belly Lake. Another 0.5 miles along the shore and you'll come to another parking area at the end of Forest Road 365. From the second parking area, the trail wanders through the woods to Mays Creek Trail #192
that merges in from the right. Almost immediately, the trail forks with Pettit Lake Cutoff Trail #041
peeling off to the left.
You'll likely want to take one of these trails as you are not allowed to ride past the wilderness boundary just ahead. You may want to lock up the bikes and hike on in, but be sure to get signed in with a free permit if you do.