Black Canyon River Drive –Take the East Portal Road from the South Rim Drive near the entrance to the park. The East Portal Road is managed by the Bureau of Reclamation. The road down the cliff is paved and two-way, but windy and very steep. Vehicles over 22 feet are prohibited. Once you get to the river, it is flat and takes you to the dam. The experience here is very different from the rim trail but if you have time, do both. The cliffs are not nearly as high as those seen from the rim, but they are a beautiful backdrop for the river.