State Route 4 (SR 4) is a state highway in the U.S. state of California, routed from Interstate 80 in the San Francisco Bay Area to State Route 89 in the Sierra Nevada. It passes through Ebbetts Pass and contains the Ebbetts Pass Scenic Byway, a National Scenic Byway.

SR 4 roughly parallels the Sacramento-San Joaquin River Delta, a popular area for boating and fishing. There are a number of accesses to marinas and other attractions.

State Route 4 is part of the California Freeway and Expressway System and is eligible for the State Scenic Highway System. However, it is only a scenic highway as designated by Caltrans from a point east of Arnold to SR 89. SR 4 is also known as the John Muir Parkway from I-80 in Hercules to I-680 near Martinez, named for the environmentalist John Muir. The stretch through Franklin Canyon was once known as "Blood Alley."

SR 4, an east–west highway, begins in Hercules at San Pablo Avenue next to the Interstate 80 junction as part of John Muir Parkway. (The actual parkway extends a bit past the western terminus.) The road is an expressway from its starting point until it approaches Martinez, at which point it becomes a full freeway (the California Delta Highway) passing Concord, Pittsburg, and Antioch. The John Muir National Historic Site is located directly north of Route 4 on Alhambra Avenue in Martinez. Alhambra Avenue at SR 4 is also the site of the Franklin Canyon Adobe. BART tracks run in the median of the freeway from the Port Chicago Highway interchange in Concord to the Bailey Road interchange in Bay Point, where the line currently ends at the Pittsburg/Bay Point Station. Access to that station is provided by a pedestrian bridge crossing over the eastbound lanes of Highway 4. After Antioch, the freeway turns southward at its intersection with State Route 160, turning into a suburban and rural road bypassing the Bay Area's outermost eastern suburbs (Oakley and Brentwood); this section is also known as the John Marsh Heritage Highway.

Route 4 east continues to Stockton, where it briefly joins I-5 and then enters a separate freeway (known locally as the Crosstown Freeway) routing almost directly through downtown Stockton. The route then runs concurrent with State Route 99 before running eastward into the Sierra through Angels Camp, one of the richest quartz mining sections of the Mother Lode and home of "The Celebrated Jumping Frog of Calaveras County", and Calaveras Big Trees State Park. The route runs through the 8,050 ft (2,450 m). Pacific Grade Summit on its way up to the 8,730 ft (2,660 m). Ebbetts Pass (being Northern California's highest road) and ends at State Route 89 ten miles (16 km) west of Topaz Lake, on the California–Nevada border. The portion from Arnold to its terminus is designated the Ebbetts Pass Scenic Byway, which is eventually one lane.

Through the mountains, SR 4 is not suitable for large trucks, buses, or RVs, as it becomes very steep and narrow, with no center dividing line shortly after the Mount Reba Turnoff to Bear Valley Ski area, with tight switchbacks. The pass is not plowed for snow, and thus closes during the winter months often from November through as late as May. Thus, no passage between the Mount Reba Turnoff and Markleeville is possible. The western slope is plowed and rarely closes, even for a few hours, but often has chain restrictions during and immediately following storms, usually just east of Arnold. The eastern slope is not plowed.

Although segments of Route 4 were part of the state highway system since 1909, Route 4 was officially designated as such between US Route 40 (now Interstate 80) and State Route 99 in 1934. Prior to that date, the then existing segment was officially known as the "Borden Highway", and the bridge over the San Joaquin River is still referred to as the "Borden Highway Bridge" in tidal tables. Construction of Route 4 did not finish until 1935, however.

The portion of Route 4 from US Route 40 to State Route 24 was added to the highway system in 1933 as Legislative Route Number (LRN) 106. East of the concurrency with State Route 24 to State Route 49, Route 4 was designated as LRN 75 from 1931-1934. Finally, the segment from State Route 49 to State Route 89 was signed as LRN 24 from 1909 to 1934.

From 2008 to 2009, a road built by the State Route 4 Bypass Authority, named the State Route 4 Bypass, opened in three phases, bypassing Route 4 in Oakley and Brentwood to the south and west. Many of the signs and local maps designated this extension as simply "Bypass Road." A section of Marsh Creek Road was widened to serve as the connection between the bypass built by the authority and the original Route 4 towards Stockton. In 2012, Caltrans handed over authority for State Route 4 in Oakley and Brentwood to the respective cities. In return, it gained control of the bypass and the upgraded section of Marsh Creek Road, which officially became State Route 4.

Only the portion of the bypass from California SR 160 to Lone Tree Way interchange is a multi-lane freeway. The portion from Lone Tree Way to Vasco Road is single-lane each way and have signal-controlled grade crossings at Sand Creek Road, Balfour Road and Marsh Creek Road. In May 2010, this narrow stretch of the road handled 27,000 to 30,000 vehicles per day. In 2011, Caltrans awarded $25 million toward upgrading the section from Lone Tree Way to Sand Creek Road to a full freeway and constructing an interchange at Sand Creek Road.

The freeway segment of Route 4 in Stockton is part of a proposed route to upgrade Route 99 into a future Interstate highway. Under one proposal, the new interstate would go along Route 99 from the split with I-5 at Wheeler Ridge north through Fresno to Stockton, where the proposed route would then turn west via the Route 4 freeway to a terminus at I-5.[citation needed]

This table reflects the transfer of the State Route 4 Bypass to Caltrans in 2012. Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.