The thirty-year period, to the start of World War II, was a time of speculation and debate about dams in the Grand Canyon, but little physical action. As that time ended, however, water was backing up into the Canyon behind Hoover dam, and silt was being dropped. investigations were being planned. In addition to the political disputes, the only check to those plans was the National Park, and perhaps the Monument. Through the various revisions to the federal power laws, the effort to keep dams out of NPS areas had finally resulted in what seemed an absolute reservation to Congress of the decision to authorize any Grand Canyon dam, if, and a big one, it would encroach on those areas. This check, however, was as much a stimulus, to engineering imaginations.
A real dam takes years to build and decades to show all its effects. Imagined ones can soar. In between, the plans are words & pictures disputed in political debates. Some matters did seem settled by the end of 1941: Arizonan schemes, on the one hand, for grandiose irrigation projects --the High Lines-- that would have taken water from Marble Gorge or around Bridge Canyon for irrigation tunnels and canals had been marginalized by the Boulder project and the success of the Colorado Compact (Arizona would ratify it unconditionally in 1944).
Proposals to generate electricity, on the other hand, proliferated, although the Girand-FPC experience and perhaps the early investigations by SoCalEdison indicated no central place for a non-governmental effort. Which, as war began, left a municipality, a state, and the central government as the prime movers. The Los Angeles Dept of Water and Power had a big market and innovative proposals. Arizona pushed its needs in Congress and the FPC (after 1944, through the Arizona Power Authority). With the success of building Hoover dam, the federal Bureau of Reclamation seemed pre-eminent.
The early staircase concept, of La Rue and others, was disrupted by the Park, though to many proponents, reservoirs could only enhance the visitor experience. The maximum elevation that Hoover's reservoir could reach into the Canyon provided a downstream end point. Since there was to be no water diversion, and provided that other dams -- above Lee's Ferry, on the Paria and Little Colorado -- controlled waterflow and silt, the only concern in planning for utilization of the mainstem in the Canyon became how to maximize power and revenue.
Building at the Bridge site to a height to reach the Park had been a favorite since the mid-1920's. (Surely, it was the ease of access down Peach Springs Canyon to Diamond Creek along with the lack of a complete survey that gave a dam near Diamond its early cachet.) As early as 1921, LADWP had put forth the idea of using a tunnel to carry power water around the Park, with a power plant just above the highest elevation of a downstream reservoir. That point became associated with Kanab Creek; thus, the Kanab Tunnel. Marble Gorge was the reach hardest to settle upon, although La Rue had found the damsites down in the Redwall stretch in 1923. However, the interest in diverting water and a competition with sites around Lee's Ferry kept the focus off the best power-dam sites in the 1920's and 30's. The latter decade also saw the complication for the downstream damsite of the Monument's being proclaimed, with its impact on FPC jurisdiction, which also changed.
The end result of these various factors in the 1950's and 60's was that, even with basic questions seemingly settled (no diversion, no staircase, etc.), though theoretically there might be a superior arrangement for optimum power generation, nothing was actually ever settled upon by all parties, as they played out the variations on dam heights & operational modes, impacts on the Canyon--NPS lands and not, LADWP, APA & Reclamation, FPC & Congress, dedication of revenues. In this, the issue of Grand Canyon damming shares with other issues a heightened tension and significance that frustrate rational, negotiated outcomes, always arousing passion and demanding drama at the highest political levels.