Trans-Sierra Highway

The Trans-Sierra Highway was a potential highway project proposed to traverse the Sierra Nevada, connecting the Central Valley of California to regions eastward. The concept, which emerged in the 1920s, was ultimately never realized due to significant resistance from environmental conservationists and local communities.

The prospective highway was intended to join Mono and Madera counties. Environmentalists, however, expressed concern that the project would pose a serious threat to the area's natural wilderness. Particularly, the highway's proposed route was expected to intersect the headwaters of the San Joaquin River, causing potential harm to the surrounding ecosystem.

Initial proposals
The initial proposals for the Trans-Sierra Highway emerged in the 1920s. Various highways across the central Sierra Nevada were put forward but none were actualized. This highlighted the growing strength of the conservationist movement.

Despite this, the relatively low elevation of Mammoth Pass continued to capture the interest of business ventures in the Central Valley. When the High Sierra and Minarets primitive areas were designated west of the Middle Fork Valley in 1931, a legislative gap was intentionally left between them to accommodate potential highway construction.

Lobbying and opposition
The possibility of a Trans-Sierra Highway resurfaced in the mid-1950s when representatives from Fresno, Madera, and Merced counties began advocating for the road. They positioned it as necessary for accessing the "rich markets to the east." Others advocated for the route as a national defense project or as an escape route from nuclear war.

A 1957 study by the Bureau of Public Roads and the US Forest Service concluded that such a road was feasible, sparking increased opposition from Mammoth area residents and laying the foundation for a local movement against the highway. Mammoth resident Genny Smith organized the local movement.

In 1966, California state highway engineer J.C. Womack concluded that the highway, while feasible, would entail high costs and environmental impacts. He pointed out the need for large bridges to cross steep canyons, high snow-removal costs, and potential damage to the Devils Postpile columns due to heavy construction. Despite his warning, some state legislators continued to support the proposal.

Environmental impact and final decision
An environmental impact statement issued in 1971 highlighted the potential "substantial adverse impacts" of the proposed road. These included the visual intrusion of retaining walls on the wilderness and the possible degradation of the fragile soils, vegetation, fish, wildlife, and timber supply in recreation areas.

In 1972, in a historic event held at a 9,200-foot Summit Meadow in the Sierra Nevada, Governor Ronald Reagan, on horseback, announced President Nixon's decision to halt the construction of the proposed Trans-Sierra Highway. Reagan had rallied against the highway alongside environmental groups, including the Sierra Club, arguing that its construction would lead to significant environmental damage. Reagan's plan was to have the region classified as an official wilderness area, which would make construction illegal. Upon receiving a telegram from the White House stating Nixon's decision, Reagan announced, "the proposed Trans-Sierra Highway will not be built". He advocated for future protection of the area to ensure that no similar projects could threaten the wilderness in the future.

Aftermath
The Trans-Sierra Highway proposal was finally put to rest with the passage of the California Wilderness Act of 1984, closing the wilderness gap and preventing the construction of any such highway in the future.