State Route 90 (SR 90) is a state highway in the U.S. state of California that consists of two unconnected pieces in Greater Los Angeles.

Most of the western portion of SR 90 is the Marina Freeway, a short freeway in southwestern Los Angeles and the nearby suburbs, linking Marina del Rey to the rest of Greater Los Angeles. SR 90 begins at Lincoln Boulevard (State Route 1) near Marina del Rey as the Marina Expressway. It then goes past a few intersections before becoming the Marina Freeway. It then continues eastward approximately along the border between the Del Rey and Westchester neighborhoods of the city of Los Angeles before terminating in Slauson Avenue in southern Culver City to just past Culver Boulevard.

The eastern portion of SR 90 runs along Imperial Highway between Beach Boulevard (State Route 39) in La Habra and State Route 91 in Anaheim Hills, also passing through Fullerton, Brea, Placentia, and Yorba Linda. The entire portion of the route through the city of Yorba Linda was relinquished to the city in 2002 and a portion of it, between Esparanza Road and Yorba Linda Boulevard is built to freeway standards. The city renamed it the Richard M. Nixon Freeway in honor of the 37th President of the United States, Richard Nixon, who was born in Yorba Linda less than half a mile away from the road.

The west segment of SR 90 begins at Lincoln Boulevard (State Route 1) in the Del Rey district of Los Angeles. It heads east along the Marina Expressway, past several intersections, and becomes the Marina Freeway after crossing Ballona Creek. After two interchanges - with Centinela Avenue and Interstate 405 - SR 90 and the freeway end at Slauson Avenue.

The east segment begins at the intersection of Imperial Highway and Beach Boulevard (State Route 39) in La Habra. It heads east and southeast on Imperial Highway, ending at State Route 91 about 1⁄4 mile (400 m) after crossing the Santa Ana River from Yorba Linda into Anaheim. A portion of the road in Yorba Linda is built to freeway standards; it is now known as the Richard M. Nixon Parkway. Caltrans relinquished the entire portion of the route through the City of Yorba Linda in 2002. However, the same state law that authorized relinquishment required the city to "maintain signs directing motorists to the continuation of Route 90".

SR 90 is part of the California Freeway and Expressway System, and is part of the National Highway System, a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration.

Legislative Route 221 (the Slauson Freeway, now the Marina Freeway) was defined in 1947 to run from pre-1964 Legislative Route 60 (now State Route 1) east to pre-1964 Legislative Route 165 (now Interstate 110). A 1959 extension took it east to pre-1964 Legislative Route 170 (now Interstate 605).

To the east, Legislative Route 176 (the Yorba Linda Freeway, now also the Marina Freeway) was defined in 1939 from pre-1964 Legislative Route 62 (now State Route 39) east and southeast to pre-1964 Legislative Route 43 (now State Route 91). A 1959 extension took it west to pre-1964 Legislative Route 174 (later State Route 42) near Norwalk.

In the 1964 renumbering, LR 221 was assigned State Route 90, but LR 176 all became part of State Route 42, along with the connecting LR 174 to the west. The piece of LR 176 between I-605 and SR 39 was reassigned to SR 90 in 1965, and the rest east to SR 91 became part of SR 90 in 1968 (at the same time as SR 42 became Interstate 105).

Originally planned as the Slauson Freeway, Route 90 was slated to extend across southern Los Angeles County and northern Orange County, ending at the Riverside Freeway in eastern Anaheim, mostly parallel to Slauson Avenue. The full route was added to the California Freeway and Expressway System in 1959. By the 1960s, community opposition had reduced it to what is effectively a minor spur of I-405 to Marina Del Rey (derisively dubbed the "Slauson Cutoff" by comedian Johnny Carson). It was renamed the Richard M. Nixon Freeway for a brief period in the early 1970s, but after Nixon's resignation in the wake of the Watergate scandal, its name was changed to the current appellation.

From I-405 west to Centinela Avenue, the Marina Freeway is 8 lanes wide, before it quickly narrows to 4 lanes at the Culver Boulevard exit. The freeway ends approximately 1⁄2 mile (800 m) west of Culver Boulevard, and continues as an expressway. There was talk of extending the Marina Expressway slightly west of Lincoln Boulevard (Route 1) to Admiralty Way (approximately 1⁄4 mile [400 m]) to accommodate ongoing expansion of the Marina Del Rey area. Strong opposition, the acquisition of surrounding properties, and potentially infringing on a public park along Admiralty, which contains a section of the Marvin Braude Bike Trail killed the proposal.

In 2002, the City of Yorba Linda assumed responsibility for Imperial Highway to complete various construction projects within city limits when the State Assembly passed AB 887; it lost its state route designation in the process and is now called the Richard M. Nixon Parkway within the city.

By 2005, construction on the western end of the Marina Freeway began, to extend the freeway terminus from Culver Boulevard to approximately 1⁄2 mile (800 m) west of Culver Boulevard by building a full interchange at Culver. The freeway extension was completed in early 2007. The freeway extension also allows Route 90 drivers to avoid a traffic signal at Alla Road (just west of Culver Boulevard.). After the end of the freeway, a pair of frontage roads operating as an expressway continues as Route 90 up to Route 1 (Lincoln Boulevard). Signalized intersections occur at Mindanao Way and Lincoln Boulevard, which is the end of the expressway in Marina del Rey. The reason for the extension is to relieve traffic congestion on surface streets.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage. R reflects a realignment in the route since then, M indicates a second realignment, L refers to an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see California postmile § Official postmile definitions). Segments that remain unconstructed or have been relinquished to local control may be omitted. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.

County	Location	Postmile	Exit	Destinations	Notes
Los Angeles LA 0.92-T3.28	Los Angeles	0.92		SR 1 (Lincoln Boulevard)	West end of SR 90
		1.20		Mindanao Way
		​	West end of freeway
		1.75		Culver Boulevard
		R1.72	1	Centinela Avenue
	Culver City	2.65	2	I-405 (San Diego Freeway) – Sacramento, Long Beach	No westbound exit to I-405 south or eastbound entrance from I-405 north; former SR 7; I-405 exit 50A northbound and 50B southbound
		​		Sepulveda Boulevard	Eastbound entrance only
		T3.28		Slauson Avenue	At-grade intersection; east end of western segment of SR 90
Gap in route
Orange ORA 0.50-12.83	La Habra	0.50		Imperial Highway	Continuation beyond SR 39
				SR 39 (Beach Boulevard) – Buena Park, Huntington Beach	West end of eastern segment of SR 90
		​		Idaho Street
		​		Euclid Street
		2.50		Harbor Boulevard – Fullerton	Former US 101 / SR 72
	Brea	4.39		Brea Boulevard
		5.19		State College Boulevard – Brea
	Fullerton–Brea line	R5.45		SR 57 (Orange Freeway) – Santa Ana, Pomona	Interchange; SR 57 exit 9
	Brea	​		Kraemer Boulevard – Placentia
		7.27		SR 142 east (Valencia Avenue) – Chino Hills, Chino	Western terminus of SR 142
	Placentia	​		Rose Drive
	Placentia–Yorba Linda line	​	East end of state maintenance
	Yorba Linda	​		Yorba Linda Boulevard – Yorba Linda
	Yorba Linda–Anaheim line	11.15		Kellogg Drive	Interchange
		12.03	West end of state maintenance
	Anaheim	12.27		Orangethorpe Avenue, Esperanza Road	Interchange
		​		La Palma Avenue
		12.83		SR 91 (Riverside Freeway) – Newport Beach, Los Angeles, Riverside, Beach Cities	Interchange; east end of SR 90; SR 91 exit 36
		12.83		Imperial Highway	Continuation beyond SR 91
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Incomplete access

• California Roads portal

• Caltrans: State Route 90 highway conditions
• Caltrans Traffic Conditions Map
• California Highway Patrol Traffic Incidents
• California @ AARoads.com - State Route 90
• California Highways: SR 90
• California Consumers Against the State Route SR 90 Extension