The California Zephyr is a passenger train operated by Amtrak between Chicago and the San Francisco Bay Area (at Emeryville), via Omaha, Denver, Salt Lake City, and Reno. At 2,438 miles (3,924 km), it is Amtrak's second longest route after the Texas Eagle's triweekly continuation from San Antonio to Los Angeles, with travel time between the termini taking approximately 51​1⁄2 hours.^[2] Amtrak claims the route as one of its most scenic, with views of the upper Colorado River valley in the Rocky Mountains, and the Sierra Nevada.^[3] The modern train is the second iteration of a train named California Zephyr; the original train was privately operated and ran on a different route through Nevada and California.

During fiscal year 2018, the California Zephyr carried 418,203 passengers, an increase of 0.7% over FY2017.^[4] The train had a total revenue of $51,950,998 in FY2016, an increase of 6.5% over FY2015.^[1]

Prior to the 1971 creation of Amtrak, three competing trains ran between Chicago and the East Bay, with bus connections to San Francisco:^{[5] []}

Railpax (renamed Amtrak in late April 1971) originally intended to revive the California Zephyr as part its original route network, using the Burlington Northern (ex-CB&Q) east of Denver, the DRG&W between Denver and Ogden, Utah, and the WP west of Ogden. The California Zephyr route served more populated areas than the Overland Route (including Denver and Salt Lake City), ran through rural communities that lacked good highway access, and could attract passengers to its scenic routes.^{[5] []} However, the WP had shed the last of its money-losing passenger service with the end of the California Zephyr, and it was not eligible to participate in Amtrak's formation. On April 12, 1971, the WP refused to cooperate with Railpax, and the SP route between Ogden and Oakland was chosen instead.^{[5] []} On April 26, the D&RGW elected not to join Amtrak; the contract specified that Amtrak could later increase service, and the railroad feared that would crowd its single-track mainline that competed with the UP's double-track route. The D&RGW chose to operate the Denver–Ogden Rio Grande Zephyr, and Amtrak scrambled to piece together a Denver–Cheyenne–Ogden routing on the UP.^{[5] []}

Between the spring of 1971 and the summer of 1972, passengers traveling between Chicago and Oakland would have to travel on two different trains: the Denver Zephyr, which operated daily between Chicago and Denver, and the City of San Francisco, which operated three times a week, between Denver and the San Francisco Bay Area. Eventually, however, after several false starts, Amtrak consolidated the two trains into one, dubbed the San Francisco Zephyr, homage to both the California Zephyr and the *San Francisco Chief,*between Chicago and Oakland. The Rio Grande continued to operate the Rio Grande Zephyr between Denver and Ogden.^{[5] []}

In 1983 the D&RGW elected to join Amtrak, citing increasing losses in passenger operations. Amtrak re-routed the San Francisco Zephyr over the D&RGW's Moffat Subdivision between Denver and Salt Lake City, its original preference from 1971. The change was scheduled for April 25, but a mudslide at Thistle, Utah closed the line and delayed the change until July 16. With the change of route, Amtrak renamed the train as the California Zephyr.^[6][7] The modern California Zephyr uses mostly the same route as the original east of Winnemucca, Nevada. The train uses the route of the former City of San Francisco, along the Overland Route (First Transcontinental Railroad), between Elko, Nevada and Sacramento. Across central Nevada, the two rail lines have been combined to use directional running. As such the exact spot the train switches lines depends on the direction of travel.^[8]

For most of the 1980s and 1990s, the California Zephyr operated in tandem with the Seattle-bound Pioneer and Los Angeles-bound Desert Wind. Since 1980, the PIoneer and Desert Wind had exchanged through coaches with the San Francisco Zephyr at Ogden. The exchange point was moved to Salt Lake City when the latter train became the California Zephyr.^{[5] []} This created a behemoth of 16 Superliner cars running from Chicago to Utah, easily the longest train Amtrak had operated. Amtrak needed at least four locomotives to pull the train through the Rockies. To ease the load, Amtrak began splitting the Pioneer from the Zephyr and Desert Wind at Denver in 1991.^{[5] []} The Pioneer and Desert Wind were both discontinued in 1997.

The western terminus of the train was cut back to Emeryville station when Oakland Central station was closed on August 5, 1994. The California Zephyr was re-extended to Oakland with the opening of the Jack London Square station on May 12, 1995. However, this required a complicated reverse move along street running tracks to reach the wye at West Oakland. The train was cut back again to Emeryville on October 26, 1997.^[9]

The west-bound train is Amtrak number 5 (eastbound, it is number 6). Upon leaving Chicago Union Station, the train travels along the Metra BNSF Railway Line, with an intermediate stop in Naperville, Illinois.

After passing through Aurora, Illinois, the train passes through the seemingly endless corn, soybean fields and small farming towns of Illinois and Iowa. The route crosses into Iowa at the Burlington Rail Bridge across the Mississippi River in Burlington, Iowa, then into Nebraska between Council Bluffs and Omaha. Overnight, and into the early morning, the train traverses Nebraska and northeastern Colorado, before making a morning arrival in Denver.

At Denver the train departs BNSF Railway-owned track. From Denver west, the train runs along the Union Pacific Railroad's Central Corridor. The scenery changes dramatically departing Denver as the train climbs the Rocky Mountains. After going through the Tunnel District, the line crosses the Continental Divide via the 6.2 mile-long Moffat Tunnel under James Peak. The tracks then follow the Colorado River, through the transition from a narrow, whitewater river (popular with rafters, who habitually moon the train as it passes) to a much wider stream past Glenwood Canyon and Interstate 70 toward Grand Junction. The train finally departs the now much larger Colorado River after exiting Ruby Canyon, which is also where the train enters Utah.

In Utah the train follows the southern rim of the Book Cliffs to their end near Helper. The train then crosses the Wasatch Mountains, cresting at Soldier Summit. After passing the Wasatch the train arrives at the Wasatch Front, where most of the population of Utah is located.

Once the train reaches Salt Lake City the train loosely follows Interstate 80 until the terminus of the train in California. Both the freeway and railroad pass along the south shore of the Great Salt Lake and across the Bonneville Salt Flats towards Nevada. So, after traveling overnight through Utah and crossing the Utah/Nevada state line at Wendover, Utah/West Wendover, Nevada, the route passes the Toano Range, via Silver Zone Pass, across the Goshute Valley, tunnels under the Pequop Mountains and then skirts the northern edge of the Ruby Mountains.

The train first reaches the Humboldt River near Wells, which the train loosely follows until the river's end in the Humboldt Sink near Lovelock. The tracks cross the center of the Forty Mile Desert; on the other side of this desert valley is the Truckee River, which provides the train's path to Reno and up the Sierra Nevada in California.

In California, the train crests the Sierra Nevada at Donner Pass and, after rounding Donner Lake, descends following a high ridge between the American and Yuba Rivers, through Emigrant Gap. Eventually, the California Zephyr reaches the lowland areas of the California Central Valley, and then along the San Pablo Bay, with stops in Sacramento and Davis. It crosses the Benicia Bridge and has stops in Martinez and Richmond. The trip ends in Emeryville, a suburb of Oakland. From Emeryville the free Emery Go Round shuttle connects passengers to the Bay Area Rapid Transit (BART) system, or a Thruway Motorcoach provides connecting service to San Francisco's Embarcadero (with sweeping city views from the San Francisco-Oakland Bay Bridge along the way).