As one of only two states in the entire Western United States, California could scarcely have been more isolated at the start of the Civil War. No transcontinental railroad or telegraph yet connected it to the rest of the country, and no battles would be fought there. Nonetheless, California proved pivotal to the Union war effort, propping up the economy with its vast gold reserves, raising huge sums for military medical assistance, and providing a high number of troops per capita.

It was never a fait accompli that California would join the Union. Though admitted as a free state as part of the Compromise of 1850, some white residents continued to illegally enslave Black people there, even as a movement arose to ban African Americans from the state altogether. At the same time, the state legislature promulgated a system that forced many Native Americans into bondage.

Pro-slavery Democrats, known locally as the Chivalry, or “Chivs,” were particularly prominent in southern California and were led by Senator William M. Gwin, who owned hundreds of slaves back in his former home state of Mississippi. In 1859, the Chiv-dominated state legislature even passed a bill that would have split California in two, with the southern half open to slavery. (The U.S. Congress never entertained the plan, thereby killing it.)

That same year, the pro-slavery chief justice of the state Supreme Court slayed a less slavery-inclined U.S. Senator from California in a duel.

“You had to be somewhat courageous to try and stir up Union sentiment in some parts of California,” says Glenna Matthews, author of “The Golden State in the Civil War: Thomas Starr King, the Republican Party, and the Birth of Modern California.” In downtown Los Angeles, for instance, “it was impossible to fly the Stars and Stripes.”

With so many Southern sympathizers around, including in the highest reaches of the Army, Confederate President Jefferson Davis purportedly expected California to devolve into crippling infighting, if not secede entirely. But he made a major miscalculation. As it turned out, his supporters, though vocal, were vastly outnumbered by other Californians who increasingly rallied to the Union cause.

Indeed, state residents responded with aplomb to a federal call for troops in the summer of 1861, immediately forming two cavalry and five infantry regiments. By the end of the Civil War, some 17,000 Californians, many of them veterans of the Gold Rush, would serve as Union soldiers out of a total population of less than 400,000. (An additional couple hundred men would join the Confederacy.)

“This is more manpower than the [West] has ever seen before,” says Andrew E. Masich, president of the Heinz History Center in Pittsburgh and author of “Civil War in the Southwest Borderlands, 1861-1867,” who points out that the California troops were in many ways superior to their Eastern counterparts.

“They can ride, they can shoot, they can live outdoors in harsh conditions,” Masich says. “They can also march faster and longer distances…and they’re certainly risktakers.” To top it off, quartermasters found them to be taller than the men in the Army of the Potomac, with bigger heads and feet.

These new California volunteers were needed, firstly, to replace the Army regulars who had been sent East to fight in the war’s major battles. Stationed throughout the West, from Kansas to Washington, California troops protected mail routes, built and repaired forts and roads, mapped largely uncharted territories, provided border security, and safeguarded supply shipments.

They also swooped into Confederate hotbeds, such as the Los Angeles region, capturing armed rebel sympathizers at gunpoint and jailing them and other criminal secessionists in places like Fort Alcatraz (later the site of the notorious prison).

The largest California-centric operation of the war kicked off in spring 1862, when 2,350 troops from the Golden State—later to be followed by around 6,000 more—began a 900-mile march from Fort Yuma in southeastern California to El Paso, Texas. Led by officer James Henry Carleton, this so-called California Column helped repel a Confederate invasion of New Mexico Territory.

Carleton and his men then went about setting up the newly formed Arizona Territory. Several veterans of the California Column were even elected to the Arizona legislature in 1864, while others served as prominent doctors, lawyers, judges, merchants, ranchers, and miners.

Outside of two skirmishes, however, they never much battled the graycoats. In fact, the entire California Column suffered only three deaths at the hands of Confederate gunfire. Instead, the men spent much of their time in Arizona waging war against the Apache, which had launched a campaign to expel Federals and Confederates alike from their territory.

Though both sides committed massacres, the Californians were particularly brutal, at one point slaughtering at least 50 Apache, including women and children, during a surprise nighttime assault on a village. On another occasion, Apache leader Mangas Coloradas was captured after being lured in under a flag of truce. According to some reports, the Californians then apparently tortured him with heated bayonets, shot him to death during an alleged escape attempt, boiled his severed head to remove the flesh, and finally shipped his skull East as a macabre, pseudoscientific souvenir.

California volunteers aggressively confronted other Indian tribes as well, perpetrating so many acts of violence—and speaking so openly of extermination—that some historians consider their actions to be part of a genocide. Records show that, from the time of the Gold Rush to just past the end of the Civil War, federal troops, state militias, and white vigilantes killed at least 9,492 to 16,094 Native Americans in California alone, many of them non-combatants.

Even when not shooting them down, armed Californians seized Native American prisoners, sold women and children into bondage, deported tribes wholesale, and engaged in systematic destruction of their food supplies, leading to countless additional deaths. A particularly notorious incident, which came to be known as the Konkow Maidu Trail of Tears, occurred in September 1863, when 461 poorly provisioned tribespeople were forcibly marched roughly 100 miles over rugged terrain. Only 277 arrived at their destination.

Of all the California soldiers in the Civil War, not all made their way East to the major theaters of the conflict. However, a group of about 500 mostly Eastern-born Californians sailed down the Pacific coast, crossed the Isthmus of Panama (prior to the construction of the canal), and eventually landed in Boston. There, the men, collectively known as the California Battalion, joined the Second Massachusetts Cavalry Regiment.

From there, the California Battalion participated in the defense of Washington, D.C., countered the lightening guerilla raids of Confederate Colonel John S. Mosby (nicknamed “the Gray Ghost”), helped oust the Confederates from the Shenandoah Valley, and contributed to the decisive siege of Petersburg. In the process, they earned the respect of their enemies, with one Confederate soldier calling the Californians “notoriously good fighters.”

Manpower, however, was just one aspect of California’s contribution to the war effort. Tens of millions of dollars’ worth of the state’s gold, shipped East by steamboat, also played a major role, a fact not lost on either Jefferson Davis or Abraham Lincoln.

At times, California troops were even ordered to drop their other duties to prospect for gold. “A tremendous amount of wealth was being uncovered in California,” Matthews says, which, though the gold bullion generally went to Northern banks, not the federal government, “reassured people that the United States was not going to bankrupt itself. And so it became easier for the U.S. government to get loans.”

Equally important, the California troops kept the gold out of rebel hands (and blocked their access to the Pacific), thus denying “the Confederacy the wealth and ports that they so desired in the West,” Masich says.

In addition to gold, Californians sent money across the country as well, using the newly installed transatlantic telegraph line. Most notably, they raised over $1.2 million—far more than any other state—for the U.S. Sanitary Commission, a precursor to the Red Cross that provided food, clothes, and medicine to sick and wounded soldiers, thereby filling a gap left open by the Army’s paltry medical establishment.

“People were remote from the fighting, yet they wanted to support the war,” Matthews says. “That was the dawn of the California ATM, as fundraisers like to think of us.”

With prominent civilians like Thomas Starr King, a Unitarian minister who had recently moved from Boston to San Francisco, drumming up support for the Sanitary Commission and the Union as a whole, California politics began to shift. In 1860, for example, Lincoln won only 32 percent of the California vote, whereas in 1864 he won 59 percent.

“To see the turnaround was extremely heartening to people,” Matthews says, adding that it kept “Northern sentiment uplifted when there were so many dark days.”

Lincoln himself was greatly appreciative of California, telling a friend that he wished to visit the “wonderful” state, and that “the production of her gold mines has been a marvel to me, and her noble stand for the Union, her generous liberal offerings to the Sanitary Commission, and her loyal representatives…have endeared [her] people to me.”