I have written before about how GNCP's far western boundary came to be (entry of 9 Sep 2010), and the mapped result. The following piece of the official 1975 map shows the boundary as the dashed black line. I have added the red crosses and the blue numbers as aids for the discussion below.
On March 1-2, I was part of a boating trip that floated past this western boundary section, giving me a chance to think about a proper boundary as I was looking at where it would lie. What I hoped to see were the landforms and their relationships, providing a view of how a defensible line would run. In summary, the boundary south of the river (1) showed up from the river as quite, and dramatically, clear. On the north side (2 & 3) the topography is not so emphatic.
Thirty-forty years ago, as we considered adding federal lands to GCNP, we were guided by the overall idea of lines that would include "all" the drainages that flowed into the Canyon itself , i.e., below the Paria and down to the Grand Wash Cliffs. Of course, with major side canyons -- the Little Colorado, Kanab, Havasu -- there were two limitations: non-federal ownership and the relevance of the drainage area to the goal of meaningfully presenting the Canyon to the public. We were handicapped then by the lack of detailed maps and, some of us, by lack of detailed experience on the land (though that has rarely seemed to matter in these debates). In the event, we did not examine closely the western Park boundary during the legislative struggle that enacted P.L. 93-620, the GCNP Enlargement Act of 1975. The Park thus ended up with a line of convenience that followed Lake Mead NRA lines in the area. Lazy move.
SOUTH OF THE RIVER (1 on the above map)
Now, 35 years later, I am suggesting what would be a better line; discussion is welcome. Here is the USGS topo representation:
For completeness, I also show the boundary south of the river along Hualapai land, following the Congressional mandate that the entire water surface from the Paria to the Grand Wash Cliffs is in Grand Canyon National Park.
The presence of Columbine Falls and of Rampart Cave (in the east side of the boundary ridge) are additional Grand Canyon features, along with the prominence of the limestones, another distinguishing characteristic. Releasing the land west of the ridge back into LMNRA, and leaving the soaring if ragged ridge-line as the Park boundary would assist in the goal of aiding public comprehension of what the Canyon encompasses. The southern curved line, although historically arbitrary, seems reasonable enough.
NORTH OF THE RIVER (2, 3 on the first map)
How did the Park get that piece of western boundary north of the Colorado? Not a pretty story. Using the BLM map below, we start with the LMNRA line out east. Proceeding west on that line following legal section lines, it runs along until it nears the rim of Tincanebitts Canyon (euphemism for "tin can of (cowboy) butts", for the container that marked the entrance to the no-smoking zone on the Sanup Plateau). The aim then seems to have switched to Follow-the-Rim, so the line leaves the section-line NRA boundary. Unfortunately for first principles, as it proceeds west, the rim no longer looks down into Grand Canyon drainages, but from Fort Garrent Point on, is above Pearce Canyon. which washes into Lake Mead, beyond the Grand Wash Cliffs. Finally, when the line reaches Snap Point (3 on the first map above), it goes back to straight lines west past the Cliffs, then drops south to the river. (Parenthetically, this BLM map is wrong; the official east-west line beyond Snap Point is another ½-mile north.)
If we are now going to follow out the idea of a line that includes only Canyon drainages, the next step is to decide where the line should climb up from the river, which ridge line of which north-side drainage it should follow. The Grand Wash Cliffs here retreat in a stepped fashion, unlike, and over a greater distance than, the south ridge. But after looking at the country, and at the map, it seems to me that one can choose a divide plausibly putting the Canyon on one side, Lake Mead-land on the other. Plausibly, if not quite unarguably. One of the arguments could be that River Mile 277, at the first R of RIVER, is a nice historical choice. Another might arise if the river map used to plot damsites before Hoover dam was built was found to show a logical crossing place.
What I chose to do, after reaching the river from the south, is to cross the river directly east as shown on the topo above, mounting up the divide to reach that white lizard-head sort of flat. At this point, it is then possible to follow along the south and east so that the Canyon is on the right, and the extended Pearce Canyon drainage on the left. See the fuchsia line on the second map above.
Visually, from the river, this ending has much less impact, as the foothills of the Grand Wash Cliffs rise and fall off to the north. But this lack of definition is nothing compared to what happens up on the Sanup, segment 3 above, virtually flat as it is. Here is the next segment of the topo maps to the east:
Well, as best I can do it, the fuchsia line divides the Grand Canyon drainages from those to Lake Mead. It winds east until it climbs up onto Fort Garrett Point, the west side of which it follows until it meets the current Park line. Lets put this all together on the BLM map:
BLM shows the current boundary as the thick stippled line on the north, and I have emphasized the west line with dots. As above, my suggestion is the fuchsia one. Now look at an overall map, courtesy of the Southern California Auto Club, with my suggestion in blue:
Not major, but not trivial. Worthwhile in order to emphasize the Park in a more natural relation to the Canyon. Certainly, there are heavier matters, such as moving the appropriate parts of the Grand Canyon - Parashant National Monument (Shivwits, Parashant-Andrus, & Whitmore) into the Park, and dealing with the anomalous status of the Kanab canyons. Still, from a personal point of view, I can acknowledge a mistake, if forty years too late, and suggest with a clear conscience taking land out of a national park.