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California State Route 203 the proposed Minaret Summit Highway

California State Route 203 is an approximately nine-mile State Highway located near Mammoth Lakes in the Sierra Nevada Mountains of Mono County.  California State Route 203 as presently configured begins at US Route 395, passes through Mammoth Lakes and terminates at the Madera County line at Minaret Summit.  What is now California State Route 203 was added to the State Highway System in 1933 as Legislative Route Number 112.  The original Mammoth Lakes State Highway ended at Lake Mary near the site of Old Mammoth and was renumbered to California State Route 203 in 1964.  The modern alignment of the highway to Minaret Summit was adopted during 1967.  

The corridor of Minaret Summit and Mammoth Pass have been subject to numerous proposed Trans-Sierra Highways.  The first corridor was proposed over Mammoth Pass following a Southern Pacific Railroad survey in 1901.  In 1931 a corridor between the Minarets Wilderness and High Sierra Peaks Wilderness was reserved by the Forest Service for possible future Trans-Sierra Highway.  

The corridor of the proposed Minaret Summit Highway was studied heavily between 1955-1967 as a possible extension of Interstate 70 from Utah to Interstate 5 near Los Banos.  An attempt to add an extension of California State Route 203 over Minaret Summit to California State Route 41 was proposed during 1968.  The 1968 proposal was followed by plans to utilize the Minaret Summit corridor as a Forest Service Road circa 1969-1971.  

The old grade of Minaret Summit Road appears as the blog cover photo before it was before being rebuilt to modern standards in 1954.  Minaret Summit Road would become part of California State Route 203 when the highway was realigned in 1967.  

Part 1; the history of California State Route 203 and the history of the Minaret Summit Highway Proposal

In 1901 the Southern Pacific Railroad surveyed a 1% grade alignment over Mammoth Pass near Minaret Summit.  A highway over Mammoth Pass from near Bass Lake in Madera County was planned.  The highway included 29 miles of then unconstructed roads originating near the vicinity of North Fork and Bass Lake in Madera County.  The highway would have had a maximum 7% grade, five new bridges over the San Joaquin River watershed and a terminal elevation cresting the Sierra Nevada Mountains at 7,900 feet above sea level.  

In 1931 the High Sierra Wilderness Area and Minarets Wilderness Area were established by the Secretary of Agriculture in Sierra National Forest and Inyo National Forest.  A corridor between the two Wilderness Areas was reserved for later development including a potential Trans-Sierra Highway.  The potential for a Trans-Sierra Highway was heavily resisted locally by residents of Mammoth circa 1931-1932.  

What is now California State Route 203 was first brought into the State Highway System in 1933 as Legislative Route Number 112 (LRN 112).  The original definition of LRN 112 was "LRN 23 (US Route 395) to Mammoth Lakes.  

The addition of LRN 112 is referenced in a 1933 Forest Service Report (courtesy the Caltrans Library) regarding Forest Routes connecting to the State Highway System.  Forest Route 81 is noted to connect to LRN 112 (Mammoth Lakes State Highway) via the crest of Minaret Summit to the area around the Middle Fork San Joaquin River.  Forest Route 81 (now Reds Meadow Road/Forest Road 03S11) is noted to have been constructed following the emergence of mining around the Middle Fork San Joaquin River.  The mines were eventually abandoned, and the road was repurposed to permit automotive travel to Devils Postpile National Monument (established on July 6, 1911).  

LRN 112 as originally configured appears on the 1935 Division of Highways map of Mono County

LRN 112 is shown to use the following alignment on the above map:

1.  An unnamed dirt road east of the modern US Route 395 on the roadway known as "Old Highway.".
2.  Mammoth Creek Road from the west side of modern US Route 395 to Old Mammoth Road.
3.  Old Mammoth Road through what is the original town site of Mammoth.
4.  Lake Mary Road to Lake Mary.

LRN 112 was codified during 1935.  LRN 112 retained the same definition it was given in 1933. 

The December 1937 California Highways & Public Works featured the recently improved LRN 112.  The highway had been through a resurfacing project which was complete on November 4, 1937.  

LRN 112 along Lake Mary Road at the east end of Twin Lakes appears as the cover photo on the July 1938 California Highways & Public Works.

A view of Lake Mary from LRN 112 appears on the cover of the September/October 1944 California Highways & Public Works.  

The January/February 1955 California Highways & Public Works featured the then recently improved Minaret Summit Road.  Minaret Summit Road is noted to originate from LRN 112 in Mammoth to the Madera County/Mono County line at the namesake summit.  The 5.5 miles of Minaret Summit Road were improved by way of being surfaced through the provisions of Federal Aid Secondary program 1195.  The surfacing project is stated to have been completed on October 29, 1954.  The article notes beyond Minaret Summit the road continues as a dirt Forest Service highway to Devils Postpile National Monument.  

The article notes the desire for a highway connecting over the crest of the Sierra Nevada Mountains to the Mammoth area was first identified in the 1870s during the early days of the community.  Pack trains departing Fresno Flats (now Oakhurst) crossed the Sierra Nevada Mountains via the San Joaquin River, Agnew Meadows and Mammoth Mountain to supply the mines around Mammoth.  Mining companies out of Mammoth are noted to have constructed a road from the community to the Middle Fork San Joaquin River via Minaret Summit in 1929.  The road was later extended to Reds Meadows and Devils Postpile National Monument upon being taken over as Forest Route 81.  

The Fresno Flats-Mammoth overland to Mammoth Pass can be seen on the 1882 Bancroft's Map of California.  

In 1955-1956, studies were begun for a Trans-Sierra Highway across Mammoth Pass.  Assembly Joint Resolution 5, adopted in 1955, asked the President and Congress to have the Mammoth Pass Road constructed as a National Defense Highway.  Environmental groups began to protest the Mammoth Pass Road in 1957 and the route was found to be feasible via study during 1958. 

In 1960 the Mammoth Pass Road was designated as Federal Aid Secondary program 962.  1961 Senate Joint Resolution 43 requested the inclusion of the road in the Forest Highway System and its construction by the Bureau of Public Roads.  A 1957 study by the Bureau of Public Roads proposed construction of the 32.8-mile gap as a Class II Forest Highway with 7% maximum grades, 32-foot paved road deck and 40 MPH design.  In 1962 Forest Route 100 was officially included in the Forest Highway System from Forest Route 74 near North Fork to Forest Route 81.

As part of the 1964 State Highway Renumbering the Legislative Route Numbers were dropped in favor of Sign Routes Designations.  LRN 112 was subsequently renumbered as "California State Route 203."  California State Route 203 initially retained the same definition from LRN 112, and it first appears on the 1964 Division of Highways Map.  

During early 1964 the existing Minarets Wilderness and High Sierra Wilderness were expanded.  The gap through which the proposed Minaret Summit Highway was located was now surrounded by fully designated wilderness areas.  Funds for a survey of a Trans-Sierra Highway out of Mammoth were appropriated in 1964.  In 1965, the Minaret Summit Highway was proposed as an all-weather highway from North Fork to Devils Postpile National Monument and Bishop by way of Sheeps Crossing 77 Corral and Granite Stairway.  

The November/December 1966 California Highways & Public Works noted the easternmost 1.5 miles of California State Route 203 was being realigned to connect with the new US Route 395 expressway. 

In 1966, a study was undertaken at the request of the State legislature (SCR 89, 1965) on the feasibility of a Trans-Sierra Highway connecting Interstate 5 west of Los Banos to the California/Nevada state line near Benton Station.  The proposed highway would pass near Califa, North Fork and Minaret Summit.  The eventual plan was to make this extension of Interstate 70.  Once the route crested the Sierra Nevada Mountains at Minaret Summit it would have gone through Crowley Lake at the about mid-point on a trestle, followed the alignment of Benton Crossing Road past Old Benton and onto the state line near US Route 6.  

The report notes that except for the 32 miles of unconstructed road between Squaw Dome and Minaret Summit a traversable route existed between the termini and within the corridor.  The Minaret Summit Highway as proposed was 239 miles in length.  The proposed highway used parts of existing California State Route 152, California State Route 99, California State Route 145, California State Route 41, California State Route 203, US Route 395, California State Route 120 and US Route 6 for a distance of 103 miles.  The report also noted that construction and maintenance costs were excessive for the low anticipated amount of winter traffic (scans below courtesy Caltrans Library).  

In 1966, construction costs for the Minaret Summit Highway were estimated at $125,000,000 with an addition $6,500,000 per year for maintenance.  In 1967, the Assembly Transportation Committee refused to include this highway in the State Highway System.  This measure effectively killed the prospects of the Minaret Summit Highway becoming part of an extension of Interstate 70 upon passage of the 1968 Federal-Aid Highway Act.  During late 1967, there were discussions regarding a tunnel under Sonora Pass (California State Route 108) which potentially could serve as a new Interstate corridor. 

On October 5, 1967, a new alignment of California State Route 203 to the Madera County/Mono County line at Minaret Summit was proposed (courtesy Caltrans Library).  

The new alignment of California State Route 203 to Minaret Summit appears in a Route Adoption report dated December 1, 1967 (courtesy Caltrans Library).  The new routing of California State Route 203 was to become effective on January 1, 1968.  The older alignment to Lake Mary was slated for relinquishment to Mono County.  The terminal highway elevation at Minaret Summit is noted to be 9,175 feet above sea level.  

The definition of California State Route 203 was altered by way of 1967 Legislative Chapter 1323.  The new State Highway Code definition was reworded as "Mono County line near Minaret Summit to US Route 395." 

In 1968 another attempt was made to put a scaled down Minaret Summit Highway in the State Highway System via Assembly Bill 1191.  The bill failed in committee due to opposition from conservation groups and Southern California legislators who did want more miles in the State Highway System to compete with their highways for funding.  

In 1969 Federal funding was allocated to build a modernized road between Minaret and Devils Postpile Road.  In 1971 there was a draft Environmental Impact Report for the construction of Forest Route 100 (images courtesy Caltrans Library) but there was considerable opposition to construction through wilderness areas.  The maps below have been altered to show the then existing Forest Service and State Highways more clearly.  

During April 1983 the Mono County Board of Supervisors voted against a Trans-Sierra Highway out of Mammoth.  The history of the Mammoth Pass/Minaret Summit Highway proposals can be observed in a report written by Ryan Dermody (courtesy Caltrans Library).

2023 Senate Bill 606, Chapter 619 authorized the relinquishment of California State Route 203 in the city of Mammoth Lakes.  Per the relinquishment agreement the city is to maintain continuation signage for California State Route 203.  

Part 2; a drive on California State Route 203

California State Route 203 westbound beings from US Route 395 exit 263 near the city of Mammoth Lakes.  

As California State Route 203 begins the highway is signed as 3 miles from Mammoth Lakes and 9 miles from the Mammoth Ski Area. 

Westbound California State Route 203 enters Mammoth Lakes as a four-lane expressway and makes a right-hand turn onto Minaret Summit Road.  

California State Route 203 westbound crosses through downtown Mammoth Lakes and begins to ascend to the Mammoth Ski Area.

California State Route 203 west of downtown Mammoth Lakes has a major junction with the Mammoth Scenic Loop.  Mammoth Scenic Loop was originally called the "Mammoth Escape Route" upon opening after being constructed following the 1980 Long Valley Earthquake.  

Westbound California State Route 203 ascends to the Mammoth Ski Area.  Despite the "END" placard assembly the highway continues west to Minaret Summit at the Madera County line.  

The Minaret Summit Vista is located an elevation of 9,265 feet above sea level.  The summit offers views of Ritter Sub-Range of the Sierra Nevada Mountains which includes the namesake Minarets.  

From the end of California State Route 203 at Minaret Summit the road continues as Inyo Forest maintained Reds Meadow Road.  Devils Postpile National Monument can be accessed from Reds Meadows Road.   The Monument is located on the Middle Fork San Joaquin River.  The Monument consists of a series of column shaped lava basalt formations that have a form resembling logs.

Version History

-  Originally published on July 5, 2017.
-  Updated on March 25, 2024. 


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