Interstate 40 forms the majority of the northern boundary to Mojave Trails National Monument, except at either end, where the preserve includes areas further north, together partly enclosing the adjacent Mojave National Preserve. In the west, the monument contains most of the Cady Mountains Wilderness Study Area
, a series of ridges and valleys, and also the Afton Canyon Natural Area
, where a short section of the Mojave River flows year round through a colorful ravine lined by banded rocks, sustaining an important riparian environment. The canyon is reached by a 3 mile graded track from I-15 exit 221, while the WSA is accessed from the south, via the rougher Crucero Road
from Ludlow on I-40 (exit 50). Old Route 66
also starts at Ludlow, initially paralleling the interstate for a short distance then heading off to the southeast, passing several tiny communities including Baghdad, Amboy, Chambless and Essex, then crossing I-40 again at exit 115 (Fenner) and finally merging with US 95 24 miles further. Along Route 66 are another four wilderness areas - Trilobite, Clipper Mountain, Piute Mountains and Bigelow Cholla Garden - all centered on mountain ranges; the former (containing the Marble Mountains) is famous for its early Cambrian trilobite fossils, while the latter, across the north edge of the Sacramento Mountains, is home to a particularly dense and extensive population of the teddy bear cholla cactus
. There are also two developed sites along the road; a picnic area and trailhead for the 1.7 mile hike across lava fields to Amboy Crater
, and similar facilities at Bonanza Spring
, another riparian area, within a scenic, half mile-long limestone canyon.