Grand Canyon's West Exit Landmarks

draft--LANDMARKS FOR THE WEST EXIT OF THE GRAND CANYON--draft

There is general agreement to use River Mile 277 as the length of the Grand Canyon. The actual location for RM 277 has changed, and it is appropriate to determine landmarks near the Colorado River that make it easy, topographically and geologically, to recognize an end point, the exit from the Grand Canyon. 

(Note: The boundary of Grand Canyon National Park (GCNP) in this western end includes lands that are not in the Canyon’s drainage, but flow further west into Lake Mead.) 

Fortunately, such landmarks do exist, and can be tied into the landforms that delineate the divides on the north and south sides of the river for the final drainages into the Canyon.

Lets start with an overall view of the west end, from the Canyon's Westernmost High Point (WHP in red on the right) on the Shivwits Plateau over to RM 277. Pearce Canyon, P,  some of it in the Park, sort of parallels the Park boundary. However, it is west-flowing, not south into the Grand Canyon drainage. The red S locates Snap Point, at present the marker for the Park boundary, but again it is not within the Canyon’s drainage.  The broad flat from WHP running toward the end at 277 is the Sanup Plateau.

On the River's south side, running south from the red 277, is the ridge that divides the Canyon’s last side canyon from the land that drains west into Lake Mead.

Across the river, to the north and east, is a jumble of small drainages dropping ~3500' from the Sanup Plateau and included within the Canyon as far around as the bend marked by 277. More about this jumble in another post.

The US Geological Survey National Map gives another view of this west end. The boundary lines double up because of the line for Grand Canyon - Parashant National Monument.

 Starting at the map's lower edge right, the Park boundary runs northwest along the south bank of the Colorado, then goes south along the Hualapai Reservation boundary and then comes back around up north again (thus making the “turkey wattle”) to wiggle along the shore to 277, where it crosses to the north side, turns east, and then notheast to Snap Point. What this makes clear is that the western Park boundary takes into the Park extraneous land that drains into Lake Mead. Fortunately, in determining landmarks for the Grand Canyon’s west exit, these extra lands do not confuse the matter.

And here’s a close-up of that map at the RM 277 location showing how the boundaries for the two National Park Service (NPS)-administered places juxtapose. The Park crosses here, one supposes, because in 1974 when NPS drew the official map for the Grand Canyon National Park Enlargement Act, 277 was at that location. The re-setting of river mileage moved 277 upstream a bit, around the bend -- a reminder that RM 277 is a human marker, not a physical one. 

Next is a better representation of the physical, using the googlemap, where the river turns and goes west in the RM 277 vicinity. Just north and south of the word "Colorado", there are two buttes, marked by red dots or blobs. The buttes are natural, of course, but are conveniently located where the current GCNP boundary crosses the river. They are thus near-perfectly placed to be the topographic markers for the river’s west exit from the Grand Canyon.

This view shows them in geographic context with their rounded tops and ledged sides dropping more abruptly on the west:

For fun, we turn the map 90 degrees left, trim and magnify it: 

The north butte is on the left: -- Paiute Waves So Long, maybe?  

The south butte, the end of the southern Grand Canyon boundary ridge, is on the right: -- Hualapai Wishes You Well, could be appropriate.

More relevant from the river runner's perspective is the next view, taken from a boat passing through the curve of the final stretch of the Canyon (and Park), with the northern, Paiute, butte ahead as the exit marker. (Photograph thanks to Tom Martin, River Runners for Wilderness; from a December 2023 trip. The southern butte at the end of the boundary ridge above Cave Canyon was not photographable.)

Conveniently, as the Canyon’s geology map shows,(courtesy of https://rclark.github.io/grand-canyon-geology/#12.58/36.12051/-113.91967), these buttes, looking across the river at each other right at the word "Colorado", are composed of representative Grand Canyon stones, Muav Limestone above Bright Angel Shale. (This map shows west over to Grapevine Wash, the boat ramp.)

On the other hand, the green, as if for emphasis, is for conglomerate of the Grand Wash Trough; the darker brown shows Quaternary landslide deposits. The pale orange shows the silt and gravel river/reservoir deposits that have geologically recently buried the older roots of the buttes.

 On some maps, this river reach is still designated “Lower Granite Gorge”; but no granite shows here. (Yet.) The last outcrop of granite and pegmatite is up near Burnt Canyon, River Mile 261; Tapeats sandstone gets to 262. History compels me to note that Bridge Canyon Dam was proposed for 236.