Boulder Canyon

Cut deeply into surrounding plateau country is a large, dry canyon. More than a hundred square miles (400 square kilometers) of mountainous desert shed their rain through this canyon during rare floods. Within the broad canyon floor is an active channel that carries most of that flood water. Through much of its length this active channel bed is covered with rounded boulders, about the size of bowling balls. Elsewhere, the bed is bare limestone bedrock, with some eroded rock mounds and pits several feet deep. The rest of the canyon floor, outside the active channel, has soil cover with grasses and brush. Canyon walls are generally steep, climbable slopes, but there are nearly vertical cliffs where the active channel runs right up against the canyon wall.

Dimensions Active channel widths commonly exceed 30 yards (30 m), while the width of the full Canyon floor is 1000-1500 feet (300-450 m). The canyon walls are about 400 feet (130 m) high.

Key Details

In torrential rains that occur several times a decade, huge volumes of water flush through the canyon over several hours or up to two days. This is accompanied by a racket of boulders bouncing and clacking their way along the streambed, carried by the flood flow.
Walking on the dry bed of loose boulders is difficult, and requires a lot of attention even in the brightest daytime. At many times it is faster to travel on the brushy canyon floor outside the main channel.
Those hiking along the dry active channel will occasionally come across colossal scour pits in the deep bed of boulders, located where past flood waters rushed against canyon walls. These pits can be 10, 20, or even 30 feet (3-10 m) deep.

Dark Canyon wall, Guadalupe Mountains, New Mexico.

Giant scour pit in boulder bed next to canyon wall.

Bedrock channel banks, Dark Canyon, New Mexico.

Parts of the canyon floor in the bedrock channel sections have been eroded especially deeply, creating closed basins where water can pool for weeks after heavy rains. These become key seasonal watering sites for wildlife or livestock, who must eventually trek elsewhere when the water dries up.
In boulder-bed sections an explorer can sometimes climb steep, yard-high (meter-high) fronts of collected boulder sheets that were in the process of spreading their way downstream until flood waters abated.

Front edge of boulder sheet -flood flow was to left.

Small cave openings at base of canyon wall.

A few small caves are exposed in the limestone canyon walls. These are short in length and bone-dry. They may rarely have a small opening in the ceiling leading to higher ground.
While the canyon runs generally west to east, it follows a very meandering path. So, early and late in the day, much of the canyon floor is shadowed by surrounding slopes and cliffs, providing relief from the direct heat of the sun.

Story Elements

This is a ready setting for a day's grueling journey up- or down-canyon in its normal dry condition, with lack of water and sun exposure as pervasive issues. Alternatively, travelers on the plateau top might have the challenge of crossing from one side of the canyon to the other, with steep, careful walks down slopes, cliffs, and difficult walking on the boulder bed all potentially there to hamper speedy movement.
The weird, cyclopean features of this landscape, as well as the knowledge of the violent action here during floods, give a strong atmosphere of abnormalcy that could bolster or contrast with themes in a story passage.
While places to hide are lacking on boulder beds and much of the bedrock active channel area, brush on other parts of the canyon floor can provide nearby surprise appearances of people or wildlife.
As a time of torrential rain breaks, viewers on the plateau top or slopes might see something unexpected floating, tumbling along in the massive flood below.
The rare roads running across the canon floor, and some of those crossing the dry river bed further downstream on the plain beyond the plateau, just run across cleared streambed rather than than over bridges. After major floods these are blocked for a while by a sheet of accumulated boulders until they can be re-cleared.
A colossal scour pit in the canyon floor might hide a threat from those approaching along the canyon floor, or be a rare source of seeping water weeks after rains. Smaller bedrock pits of various sizes might be trap points for heavy objects/materials being carried along in abating flood waters, to be found later. Small caves in the canyon walls might serve a flotsam-collecting function, as well.
Large rock basin pools sought for drinking water by wildlife and/or cattle may also attract predators, hunters, rustlers. Much can be made of the suspense whether a particular known basin location, sought in a desperate trek, will hold water or be bone-dry.
Some of the caves in the canyon walls are large enough serves as cramped campsites for individuals or, more rarely, small groups. The irregular, uneven-floored, form of these caves, with additional smaller cavities in the cave walls and ceilings, could make for some unusual sitting/sleeping positions and weird light/shadow effects from a light source.
A story might give special significance to patches of the canyon floor being in and out of direct sunlight. Some wildlife may only come out in shade; reptiles might seek sunlight at shade's edge to sun themselves. For travelers, these different canyon floor sections will likely correspond to times of rest or greater activity. There is potential for dramatic change in visibility of distant objects or marks on canyon walls as the sun moves.
For some fantastic reason, in dry weather, a flood from these mostly uninhabited mountains might burst out of the canyon mouth onto the populated plain further downstream.

Reference Location

Dark Canyon, Eddy Co., New Mexico. There is a public road that traces part of the canyon floor, but the land beyond the road, including the active channel, is a checkerboard patchwork of private, state-deeded, and Bureau of Land Management properties. Only the BLM land allows access to the public, and even that may have fences for livestock control, which should be left undamaged. Nearby within five miles (8 km) is the much smaller channel of the Desert Streambed Throughway scene, and the same mountain range also hosts the Oasis and Decorated High Gallery scenes.