These are the relevant parts of the 1934 Navajo Boundary Act:
a) the Navajo IR goes along the south bank;
b) excluded are lands withdrawn for power (dams);
c) nevertheless the Navajo have exclusive use and occupancy of withdrawn lands;
d) until those lands "shall be required for power purposes";
e) or required for "other uses under the authority of the United States".
These phrases point to the Secretaries of the Interior as chief authority in positioning the federal executive on this matter. With scrambled purposes, just like the 1934 Act, they wore three masks: Indian Affairs (Navajo IR), Reclamation (hydro-power), and NPS.
What my two previous posts showed was that donning his Indian Affairs mask, the Navajo policy consistently was placing the western IR boundary to the river's edge . Most recently, any NPS extension to the Marble rim was subject to Navajo agreement, concurrence. On their own, the Navajo opposed Marble Canyon Dam and later established a Tribal Park on their Marble lands. This history gives enduring life to a & c of the above list.
With his Reclamation mask on (I leave to the reader the exercise of what these masks look like), the Secretary went for a Marble dam, and got beat. He then reversed course, and in 1969 sponsored a Presidential proclamation that revoked the withdrawals as it created a National Monument that ended Federal Power Commission jurisdiction. This history eliminated from national policy b & d of the1934 list.
Wearing his NPS mask, the Secretary, with the President and Congress as necessary, for 45 years included the southern part of Marble in Park schemes. Then in 1927, he gave up any NPS land on Marble's east side, wearing his Indian Affairs mask to receive it for the Reservation. Then another twist, and in the 1969 Proclamation, he switched his I. A. mask to his NPS mask, marking the easterly boundary of Marble Monument as "the easternmost limits of the lands within such reservations and withdrawals". That is, he invoked item e above to award lands next to the river to NPS jurisdiction.
He could have worn his Indian Affairs mask, and followed the historically and logically justified route of placing the NM/Navajo boundary on the eastern river shore as he revoked those withdrawals. I do not know why he flew in the face of such an obvious move. It is very clear that he obtained his NPS objectives by including the river and the west side of Marble in a Monument. It was on the map, NPS had jurisdiction, and no dam could be built unless Congress o.k.ed it. The east side was not "required" in order to serve these three "other uses".
So the Secretary made a mistake. He should have used the 1969 Proclamation to reaffirm the Navajo boundary after revoking the withdrawals. He should have explicitly recognized Navajo priority. He still could, and maybe should, but whatever, NPS has no claim to Marble's east side. It belongs to the Navajo.
By the way, I notice that slapping on his USGS mask, the Secretary did the right thing when drawing the topo maps for Marble, running the boundary down the left bank. Meanwhile, that NPS mask was blushing with the shame of not being able to prove that the east side was required for its uses. Let me count the ways.
NPS gave up the southern part of Marble in 1927. Marble was never part of any of its proposals to add lands to the Park after that. While the Navajo and Reclamation entered Marble to show their interest, NPS did not. When the crucial question of whether to build a dam in Marble was raised and fought out, NPS was on the sidelines. Directors Wirth and Hartzog never stood up for Marble's integrity, arguing a dam was inappropriate in the Canyon. Nor did Superintendent Stricklin. Nor did any group of NPS rangers or interpreters or administrators or employees organize and sign a petition protesting building a dam in this Park-worthy introduction to the Grand Canyon, even as the Navajo did oppose it publicly. (And, by the way, as an earlier Director, Newton Drury, successfully did with the dreaded Kanab power tunnel, and due to his stand, forced the Secretary in that instance to see the land through his NPS mask, not his Reclamation mask.)
And even after the Monument and its absorption into the Park, did the Secretary put on his NPS mask and show how Marble was "required"? Did he or his surrogate, GCNP, use sec. 6 of the Park Enlargement Act to cooperate with the Navajo on presenting Marble as an integral part of the Grand Canyon (educating people about that integrity certainly is a required use, still unfulfilled), building facilities and operating programs to that end? Did it work with the Navajo on a unified wilderness policy? No.
In fact and law, the only "other use" "required" is affirming the Navajo IR's boundary on the river. I do not know what activities the Navajo carry out on the lands in question. It does not affect their ownership, but what about wilderness? Could not the Navajo, having set up a Tribal Park, take the next step and use their jurisdiction to ensure Marble Canyon's wild, natural character, even as they plan motorless river trips from Lee's to the LCR? Not requiring a mask, the Navajo could show NPS the way.