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

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 John Muir National Historic Site is located directly north of Route 4 on Alhambra Avenue in Martinez.

Through the mountains, SR 4 is not suitable for large trucks, buses, or RVs, as it becomes very steep and eventually single-track, with no center dividing line shortly after the Mount Reba Turnoff to Bear Valley Ski area, with tight switchbacks.

Ebbetts Pass is not plowed for snow, and thus closes during the winter months, often from November through as late as May, blocking through traffic between the Mount Reba Turnoff and Markleeville.

In December 2016, the Crosstown Freeway west of I-5 (though technically not part of SR 4) was extended to Navy Drive via a viaduct bypassing the Boggs Tract neighborhood in Stockton.

[18] Despite being in the planning books for decades, it is unclear if the Crosstown Freeway past Navy Drive will ever be extended to SR 4 west of Stockton.

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 return, it gained control of the bypass and the upgraded section of Marsh Creek Road, which officially became State Route 4.

[21] In 2004 voters passed a half cent tax increase to fund widening from 4 to 8 lanes from Loveridge Road to Hwy 160.

[26] In 2016, Pittsburg moved to install surveillance cameras along their portion of the route, in response to a series of 20 freeway shootings in the area that had taken the lives of six people, and injured 11, in the past year.

[27] 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.

It was established in August 2013 to attract customers to businesses along the parent route's former alignment, prior to the completion of the Angels Camp Bypass.