Half a mile down the dirt road from Kolob Terrace Road, you find this gate barring further legal access. What you can do, however, is hike along the fenceline to reach the north ridge of Cave Knoll. This is a little longer than the direct bushwhack, but the fence is clear of brush for a few feet on both sides, and this is thus an easier way to attain the ridge.
Zion National Park, UT