Precursors El Camino Real Long before
California entered statehood, the 16th-century
Alta California had a loose-knit network of transportation paths deemed by the
monarchy of Spain as , or "royal roads". In the late 18th century,
Gaspar de Portolá, under the stewardship of
Junípero Serra, led Spanish missionaries on
two expeditionary runs in the coastal regions;
missions, pueblos and presidios were also established between
San Diego and
Monterey during this time. Six years after Portolá's last expedition,
Juan Bautista de Anza followed Portolá's trail from present-day Los Angeles to the
Presidio of San Francisco.
George Wharton James's 1908 travelogue ''Through Ramona's Country'' describes the road these expeditions traced out;
El Camino Real then became synonymous with it. Despite modest improvements in the mid-19th century, El Camino Real was difficult for stagecoaches and freight wagons to navigate. The movement to preserve and memorialize El Camino Real began in 1902, when Anna Pitcher of
Pasadena presented a plan to restore the route. Later that year, the
California Federation of Women's Clubs adopted the project; government agencies and other organizations signed on as well. In 1904, the
Los Angeles Chamber of Commerce formed a convention to support commemorating El Camino Real; a second convention was held in Santa Barbara that same year. The first distinctive bells marking El Camino Real were erected in 1906 and in 1915, the
Automobile Club of Southern California produced a map detailing El Camino Real and the missions. In 1924, a roadway that would eventually become part of US 101 replaced an outdated segment of El Camino Real in Ventura;
the replaced segment was later re-signed as part of SR 1. El Camino Real was part of the
Pacific Highway, a chain of highways that existed until 1926. The route was declared
California Historical Landmark No. 784 in 1963, the same year the state assumed maintenance of the bell markers. The route was also codified in the
California Streets and Highways Code.
Redwood Highway Prior to the 20th century, almost all commerce on the
Redwood Coast was done by sea, whereupon ships would dock at portside towns to transport passengers and deliver and receive goods. In 1910, the California government passed the
State Highway Bond Act, authorizing funds for a statewide road system. with another section constructed on tidal wetlands bordering
Humboldt Bay between 1918 and 1919. In 1921,
Crescent City hotelier A.D. Lee proposed the name Redwood Highway to honor
Save the Redwoods League and their work preserving redwood forests in the area. Local communities and the city of San Francisco endorsed the proposal, which was adopted in 1957. The
California Highway Commission also set stringent limits on the number of trees that could be cleared during the highway's construction, while the trees that were cut down were often used as guardrails, drainage control devices, Ultimately, increased awareness of the destruction of the redwoods led to the establishment of
Redwood National Park. Landslides and washouts repeatedly frustrated progress on Redwood Highway, with overall construction lasting about nine years, during which the highway opened segment by segment. The first paved section opened in Ukiah, after which
Jack London became the first person to ride the stretch on his way to Crescent City. and the full highway opened on October 29. To boost tourism in the area, the Redwood Highway Association marketed the highway's beauty, most successfully with the internationally publicized
Redwood Highway Marathon, held in 1927 and 1928. The
National Automobile Club also surveyed a split route for Redwood Highway in 1928, but it was not adopted.
Hollywood Freeway In 1924, Los Angeles voters backed the
Major Traffic Street Plan to address the city's worsening traffic congestion. A "stop-free express highway" between
downtown Los Angeles and the
San Fernando Valley via the
Cahuenga Pass was included in the project and the city acquired many residential and commercial properties to make room for it.
Creation The
American Association of State Highway Officials announced its intent to establish US 101 in California in 1925. The highway was originally envisioned to start at the
Mexican border at
Tijuana and continue for to the Oregon state line south of
Brookings, aligning with the future Hollywood Freeway as well as
State Legislative Routes 1 and 2 and also occupying El Camino Real and all but the Crescent City–Grants Pass section of Redwood Highway. With this alignment, US 101 would be the westernmost route in the
United States Numbered Highway System. The numerical selection for US 101 proved problematic in that it ran afoul with the system's three-digit number conventions. However, because 101 was the only odd number assigned west of
US 99, to follow conventions the numeral 101 is treated as having two digits instead of three: a 10 and a 1. The US 101 designation received its official approval on November 11, 1926, its routing in California mostly unchanged from the conceptual phase. US 101
traffic signs were erected by the
Automobile Club of Southern California in southern California and
California State Automobile Association in the north. The first signs were placed the San Diego–Los Angeles segment in January 1928, with the rest placed that summer.
Mexican border to Los Angeles At its inception, US 101 traversed
San Diego suburbs on Beyer Boulevard in
San Ysidro, Broadway in
Chula Vista, and National City Boulevard in
National City. From there, it took an erratic path through the city, coming within a few blocks of
Balboa Park before turning west and traveling through
downtown, then turning north onto India Street. North of
Mission Bay, US 101 turned west through
Pacific Beach, before turning back north on La Jolla Boulevard and serving the business areas of
La Jolla. By the 1940s, however, the downtown section was truncated onto Harbor Drive close to the
San Diego Bay and the La Jolla segment rerouted inland on Rose Canyon Road. In
Del Mar, US 101 aligned with the
Torrey Pines bypass, dubbed the Million Dollar Highway and built in 1933 to bypass a dangerous highway that predated federal designations. Also in this area, the route traversed the
Surf Line and Los Peñasquitos Creek estuary via bridges, after which, it continued along the Pacific Coast through
Solana Beach,
Encinitas,
Carlsbad, and
Oceanside. US 101 continued past
Marine Corps Base Camp Pendleton, where it entered
Orange County and passed through
San Clemente. At Doheny Park north of San Clemente, US 101 originally split into two routes, with US 101 Alternate serving the beachside cities before converging with the main route in
Oxnard, while the main route veered inland through
San Juan Capistrano,
Laguna Niguel, and
Mission Viejo, after which it zigzagged through
Irvine and
Tustin, with a concentrated section in Tustin once containing the
Tustin Garage and up to ten fuel stations for motorists traveling from the south. North of Tustin, US 101 followed
Katella Avenue and
Spadra Road, then traversed southeastern Los Angeles County on Montebello Boulevard and entered Los Angeles on
Whittier Boulevard. Due to increased traffic, US 101 between Carlsbad and Oceanside was rolled over to
Interstate 5 in the 1950s. and in 1964, California both
streamlined its numbered routes across the state and stipulated that U.S. highways be removed in favor of
Interstate highways. As a result,
I-5 supplanted US 101 entirely from Los Angeles to the Mexican border, after which, many of US 101's original surface roads were relinquished for municipal and county control. The section through Camp Pendleton was closed off to the public, The Downtown Slot also opened in 1954, Proposed interchanges with the
Beverly Hills Freeway near
Glendale, with the never built
Malibu Freeway near
Malibu Canyon, and with the never built
Laurel Canyon Freeway at the
Hollywood Split were cancelled in response to the
freeway revolts in the 1960s and 1970s. In 1952, the State Highway Commission announced plans for a freeway along El Camino Real through Los Angeles's
San Fernando Valley. between
Sepulveda Boulevard and the western city limit, was constructed and opened in segments between from 1956 to 1960, The
Conejo Grade was built as part of this upgrade; it replaced a windy two-lane road built in 1914. Grade separation in
Camarillo was also part of the upgrade; completed in 1954, it eliminated the last railroad crossing on US 101 between Los Angeles and San Francisco. West of Santa Barbara, US 101 traversed the Gaviota Pass, which was originally part of El Camino Real and was declared
California Historic Landmark No. 248 in 1937. The
Gaviota Tunnel opened to northbound traffic in the pass in 1953, with the previous road repurposed for southbound traffic. By 1954, the entire freeway was upgraded to expressway standards through the pass. North of Gaviota, bypasses funded by the
Collier–Burns Highway Act of 1947 allowed US 101 to bypass most town centers by the 1950s, although a US 101/SR 1 interchange was constructed in
Las Cruces in 1967, destroying the town. Conversely, a 1951 study determined that frontage-road businesses along a new Santa Barbara–Buellton alignment saw minimal impact on the businesses' customer volume. This combined with improvements into
Santa Ynez Valley lengthened US 101 by , but shortened travel time because it allowed for higher speeds. In the northern central coast, the
Prunedale Cutoff replaced a more hazardous route over the
Gabilan Range via the
San Juan Grade in 1932 and the
Cuesta Pass opened as an expressway in 1938. In
Salinas, US 101 was built as a freeway for by 1954; the Sala Road interchange, adopted in 1964, connected to this segment.
San Francisco Bay area Bayshore Highway, located on the San Francisco peninsula, was completed in 1929, the first section opened being a
tolled arterial between
San Bruno and
Visitacion Valley. Between 1929 and 1936, Additional ferries traversed the
Golden Gate prior to completion of the
Golden Gate Bridge in 1937. In 1936, US 101 on the San Francisco Peninsula was truncated at Bayshore Highway, while El Camino Real was re-signed as US 101 Alternate. However, due to local outrage, this section of US 101 was reverted to El Camino Real two years later, while Bayshore Highway was renamed US 101 Bypass. US 101E was also re-signed as
SR 17 during this time. Bayshore Highway was upgraded to a freeway starting in 1940. The first segment, a stretch between
San Mateo and
Burlingame, was completed in 1947, making it the Bay Area's first freeway. The freeway was extended to San Jose and San Francisco in 1962, after which it was designated part of US 101 while El Camino Real was re-signed as
SR 82. Plans to build a direct connection to the Golden Gate Bridge on the
Central Freeway, a northerly continuation of the Bayshore Freeway, were canceled in 1959 due to backlash by residents; as a result, only one section of this segment of US 101 was completed. In
Marin County, US 101's Sausalito–San Rafael segment was completed in the early 1930s, concluding with a redwood bridge over
Richardson Bay. Twin bores of the Waldo Tunnel, which connect
Sausalito and
Marin City at the highest point of the
Waldo Grade, opened individually in 1937 and 1954, and the bridge across Richardson Bay was replaced in 1956. Additionally, numerous
North Bay improvements in the 1950s centered on upgrading US 101 from expressway to freeway, as well as bypassing cities. An exception was
Santa Rosa, where US 101 was routed through the city; even so, it was brought to full freeway standards with the completion of the Steele Lane interchange in 1965. Additional bypasses were constructed in
Novato and
Geyserville in the 1970s. In
Santa Clara County, a four-lane alignment replaced a winding roadway across the
Pajaro River in
Sargent in the early 1940s and a bypass through the southern
Santa Clara Valley was adopted in 1961 and constructed in the early 1970s.
Northern California While Redwood Highway was completed in 1926, and a new 1940s alignment in
Piercy lowered the segment's total curvature from 2,978 degrees to 807. Despite these and other upgrades, freeway and expressway segments are not as prevalent on US 101 in this area compared to elsewhere. A variety of factors, most of which came into play in the middle of the 20th century, contributed to this, most notably local business owners opposed bypasses and conservationists opposed the destruction construction of a multi-lane highway would require. Conversely, the Eureka-based
Times-Standard as well as several local taxpayer groups supported the improved safety that upgrades would bring. The
Redwood Empire Association also urged the State Highway Commission to not truncate US 101 outside state park boundaries. Ridgewood Grade, located in Mendocino County and opened in 1954, was the first section of Redwood Highway upgraded to expressway. The following year, Assemblyman
Frank P. Belotti introduced legislation that would allot $10 million from the state parks' funds towards a bypass through
Humboldt Redwoods State Park. Governor
Goodwin Knight later vetoed the bill, after which the two sides agreed to expand the bypass to around the park and only remove trees with heights less than . This bypass was completed in the 1960s at an estimated $36 million , while the old alignment, known as the
Avenue of the Giants, became SR 254. In
Eureka, the Big Lagoon trestle was demolished in favor of embankments carrying a expressway, which opened in 1959 at a cost of $1.84 million . Additionally, the Arcata–Trinidad freeway located north of Eureka was completed by the early 1960s, as was a second freeway section from
Hydesville to south of Eureka with bypasses at
Fortuna and
Loleta; the southern segment was later augmented by the Herrick Avenue interchange in 1984. Elsewhere along Redwood Highway, a freeway upgrade was completed in
Ukiah in 1965, then extended north through
Redwood Valley in the late 1980s, and a $1 million , thirteen-span viaduct opened across the
Eel River in 1964. Additionally, numerous bridges were damaged during the
Christmas flood of 1964, each of which was repaired or replaced by the following March, the last being a new construction that replaced Douglas Memorial Bridge over the
Klamath River.
Modern developments Los Angeles and the Central Coast The last traffic signal on US 101 between Los Angeles and San Francisco, located in Santa Barbara, was removed in 1991. A lane was added in both directions of the
Ventura Freeway in the 1990s, eliminating several bottlenecks, and new lanes and truck pullouts were added to the Cuesta Grade in 2004 as well. Three interchanges were also added in Prunedale in 2014. Construction of the
Wallis Annenberg Wildlife Crossing also began in 2024; this crossing, a vegetated overpass spanning the Ventura Freeway in Agoura Hills, will connect the
Santa Monica Mountains with the
Simi Hills and upon completion will be the largest
wildlife crossing in the world.
San Francisco bay area In 1984, San Mateo and Santa Clara County residents voted to use sales tax funds to fund high-occupancy vehicle (HOV) lanes on US 101 in their counties. These lanes were extended through San Jose and into Morgan Hill by 2000 and the Mountain View–Redwood City section was converted to high-occupancy toll lanes in 2022, Furthermore, US 101 was expanded to eight lanes between
SR 85 in San Jose and Cochrane Road Morgan Hill in 2003 and a new interchange at Bailey Avenue, planned since the 1970s, opened in 2004. The
1989 Loma Prieta earthquake caused severe damage to San Francisco's Central Freeway, prompting its immediate closure. In 1997, a narrow majority of residents voted to rebuild the freeway; however, another vote the following year saw the majority vote for it to be dismantled, and this vote was affirmed the year after that. Demolition was completed by 2005 and the vacated right-of-way was redeveloped into
Octavia Boulevard. In 2000, Caltrans and the
Metropolitan Transportation Commission unveiled a joint plan to build continuous HOV lanes on US 101 throughout the North Bay. At the time, facilities were already existent in Marin County, having been converted from
contraflow bus lanes in the 1980s, but a gap at San Rafael was not filled until 2011. HOV lanes opened in Sonoma County in 2022 and the final segment between Petaluma and Sonoma County opened in 2025; these segments were also part of a separate 30-year, $1.5 billion US 101 improvement project that was completed in 2025. As part of this project, HOV lanes were built between between
Novato and
Sonoma County, the entire route between Novato and Petaluma was upgraded to freeway standards, and new bridges were built across the
San Antonio Creek and
Petaluma River. In 2009, a project began to replace
US 101's Golden Gate Bridge approach through the Presidio. The new Presidio Parkway incorporated two sets of tunnels and opened in 2015, while the Presidio Tunnel Tops recreational area, located above the tunnels, opened in 2022. Also in 2022,
San Francisco Municipal Railway built center bus lanes and landscaped medians on US 101's Van Ness Avenue segment as part of the
Van Ness Bus Rapid Transit project.
Northern California US 101 was truncated onto a new alignment through
Prairie Creek Redwoods State Park from the late 1980s to early 1990s. In 2009, a section of US 101 north of Leggett was moved across the
Eel River via the
Confusion Hill Bridges in order to prevent the infrequent but expensive winter closures that occurred along the old alignment. This project, controversial because it re-routed US 101 through protected wetlands, cost $459 million , included a viaduct across a flood plain, and re-located the US 101/SR 20 interchange from inside city limits to south of the city. , the remainder of the old route was still part of the state highway system, under the designation 101U (for unrelinquished).
Future In Los Angeles, two plans to
cap US 101 have been proposed: one
downtown, and the other in
Hollywood. wit the Hollywood freeway cap estimated to cost $1 billion in 2015 and the downtown cap $180 million in 2017 . with an expected completion date of December 2028, and improvements between Cuesta Grade and the northern county line are also under study. In
Monterey County, preliminary work on multiple improvements to an stretch between
Salinas and
Chualar, the result of which would upgrade the corridor from expressway to freeway, began in 2024, with construction scheduled to begin in 2031. The US 101-
SR 156 interchange has also been proposed for reconstruction and US 101 upgraded from expressway to freeway through it. and the county also has plans to add of express lanes between
I-380 and the north county line, after which US 101's express lanes would span the entire county. US 101's HOT lanes are also planned to be extended south from
Mountain View to
I-880 in 2026, while a $135 million construction project to improve the US 101/
SR 25 interchange began in 2025 with an expected completion in 2027. In more long term plans, several proposals have been made to address
sea level rise on a particularly vulnerable stretch of US 101 in
Marin City by 2050. In northern California,
Caltrans determined in 2000 that a bypass around
Richardson Grove State Park was cost-prohibitive and instead recommended the section be realigned in compliance with the
Surface Transportation Assistance Act of 1982, but , the re-alignment had not begun. Caltrans has also proposed a tunnel between Klamath and Crescent City that would replace a windy segment prone to
erosion and landslides; it was estimated to cost $2 billion in 2026. Smaller projects in northern California include fixing a portion of US 101 slipping into the
South Fork Eel River near the Mendocino-Humboldt county line. ==Names and memorials==