The second Grand Canyon National Monument was a haunted creation. Discovered and coveted by enterprising NPS staff in the 1920's for its myriad displays of how vulcanism has affected the Canyon and for the plunging view from Toroweap, encompassing parts of three more plateaus the Canyon has dug into, it was an object of loathing by stockmen and dam-builders from the day President Hoover proclaimed it in Dec 1932. Take a look at this contested space:
We start in 1932 with the red line drawn around about 273 Kac (thousand acres). The area stockmen, with Senator Hayden of Arizona leading the charge, spent the next 8 years trying to pass a law to take land out of the Monument. Their goal was the proposed black line running from west to east. It would have removed almost all of the affected grazing lands, about 150 Kac. The legislation failed, but President Roosevelt took action in 1940 by issuing an executive order removing the lands north of the brown line, a line NPS preferred, leaving the Monument at 197 Kac. However, that boundary did not satisfy opponents, and from the 1950's to 1973, there was pressure to remove the three areas A, B & C, indicated by diagonal lines, about 38 Kac. That effort was thwarted by the 1975 Park Enlargement Act, although the Act did repatriate the plateau southeast of the blue line to the Havasupai. The Act also fixed the Park boundary on the Colorado's south bank. Then in 1999, President Clinton restored a kind of Monument status by proclaiming Grand Canyon - Parashant NM, its eastern boundary indicated by green. This gave the upper end of Toroweap (or Tuweep) Valley recognition, even if not Park status.
So for the moment, Segment K (between the red marks) of the Park follows the boundary set for the Monument in 1940, as shown on the Park Act map:
The citation for Roosevelt's order setting the boundary is Proclamation 2393, 3 CFR 150 (1938-43) reprinted in 54 Stat. 2692 (Apr 4, 1940).