To find the trailhead, drive south for about 2.5 miles on a dirt road that begins immediately after the parking area for Bunchgrass Overlook. At the beginning of this road and to the west is an old cinder cone called Hippo Butte. After about 2.5 miles, there is a small turnout on the west side of the dirt road that is the parking area for the trail. The trailhead is easily located at about the midway point of the turnout.
Initially, the trail follows the same path as the Mammoth Crater Trail
. However, before reaching Mammoth Crater, the trail turns south and moves along the crater's rim. The trail then begins turning north along the crater's rim where it reaches a fork, which is the point at which the loop for Big Nasty Trail begins and ends. Either continue north along the loop or turn west along the loop. Either way the trail returns to this point. After completing the loop, continue back along the rim of the crater to the trailhead.
The trail is open and exposed like nearly all of the trails in the monument. Nevertheless, as the trail skirts the southern boundary of the monument, it nears Modoc National Forest. Thus, giant Ponderosa Pines sporadically dot much of the trail. The trail is named for a brush covered lava flow to the north of the loop. Someone, somewhere, at some time, someone said: "it is big, and it is nasty!"