Eight pages into “The Rush: California Gold, the Civil War, and the Making of the Modern World” (Viking), Nathaniel Philbrick tells us why he wrote it. Philbrick, who is seventy years old, has lived for the past four decades on Nantucket, a home that has doubled as the wellspring of his career. After publishing two books about its history—“Away Off Shore: Nantucket Island and Its People, 1602-1890” and “Abram’s Eyes: The Native American Legacy of Nantucket Island”—he turned his attention to one of the countless whaling ships that sailed forth from the island in the nineteenth century.

This was the Essex, which weighed anchor there in 1819 and was subsequently destroyed by a sperm whale in the middle of the Pacific Ocean, stranding its steadily dwindling number of crew members at sea for three horror-filled months and inspiring Herman Melville’s “Moby-Dick.”Philbrick’s own gripping narrative of the fate of the Essex, “In the Heart of the Sea,” marked a turning point in his career. It won a National Book Award, in 2000, spent forty weeks on the New York best-seller list, was adapted into a Hollywood movie, and made its author an eminence in the field of Dad History.

Philbrick’s subsequent books include popular-in-both-senses accounts of the Mayflower, the Battle of Bunker Hill, and the Battle of Yorktown. With one exception, a book about the Battle of the Little Bighorn, they have been set on the East Coast or on the ocean or both, natural enough contexts for a man who has spent most of his life on an island off the coast of New England.

So why California all of a sudden? Because, Philbrick tells us, so many Nantucketers before him developed an abrupt interest in it, too. After gold was discovered in the foothills of the Sierra Nevada, men who were born and raised to make their living from the sea sailed their whaleships fourteen thousand miles to San Francisco, abandoned them in the harbor, and rushed inland to try to make their living from the ground instead. “Over the course of nine months in 1849,” Philbrick writes, “Nantucket, once the whaling capital of the world, lost a quarter of its voting population to the goldfields.”

That is a staggering fact, one that drags behind it a whole ghost book about what happened to Nantucket and countless other places across the country after so many of their citizens left to try to strike it rich in California.

This is not Philbrick’s subject, but almost everything else is. “The Rush” is a sprawling book, characters and stories spilling out everywhere, as dense with claims as the goldfields it describes. Of these, two emerge as dominant. The first, which is woven throughout the book—albeit in the strict sense that it keeps appearing and disappearing—is that the discovery of gold in California set off a mad scramble for wealth, land, labor, and power that contributed to the onset of the Civil War and then helped determine its outcome.

The second is that what mattered most about the gold rush was not the gold but the rush. The headlong haste with which those Nantucket whalers picked up their lives and went West was representative, Philbrick argues, of a new and distinctly American appetite for speed, novelty, and transformation, one that has defined our character and shaped our future from the time of the forty-niners to the planned Anthropic I.P.O.

“The Rush” is not particularly convincing about either of these claims. This is partly because both are a little rickety and partly because they are too different to comfortably coexist in a single book: one is about history and causality, the other is about psychology and culture. Mostly, though, it is because Philbrick keeps veering off into a larger, messier, less instrumentalized account of the gold rush and its aftermath. A better title for his book would be “A History of California, 1848-1878.”

Lest that strike you as dull, consider that those are three of the most thrilling, harrowing, and action-packed decades since the founding of our nation. In a sense, then, the tacit question “The Rush” asks is not about the history it covers but about history in general: Does the past need to explain the present to be worthy of our attention?

If you know anything at all about the gold rush, you’ve likely heard the story of Sutter’s Mill, whose construction on the banks of the American River unearthed the shining flecks that, in January, 1848, kicked off the whole adventure. Philbrick, who understands that what happened next had less to do with good luck than with force, influence, and cunning, swiftly turns away from John Sutter, who never got rich off the wealth beneath his mill, to introduce a man named Samuel Brannan.

At the time, Brannan was the leader of San Francisco’s Mormon community, though no one who subsequently knew him would have called him godly. When he heard about the discovery at Sutter’s Mill, he did not head toward the mountains. Instead, he bought up every pick and shovel he could lay his hands on, then paraded through town waving around gold dust and telling anyone who would listen where to find it. In short order, Philbrick writes, San Francisco was half empty and “Brannan was on his way to becoming a millionaire.”

When Brigham Young caught wind of all this and asked his West Coast emissary to remit the appropriate tithe, Brannan supposedly told him to have God send the receipt. That was the end of his stint as a Mormon.

News of the gold spread fast, not least because people kept discovering more of it. In most places on Earth, gold is sparsely distributed, averaging around five parts per billion. But, in the California Mother Lode, a hundred-and-fifty-mile stretch of the Sierra Nevada, you could find it almost everywhere: in extant streams and ancient riverbeds, in gravel bars and veins of quartz, in sand and soil and silt and sometimes, on a very good day, just sitting there.

By the end of 1848, it seemed that half the nation was dreaming of going West to claim a share of it. But there was a problem: the available steamboat and railroad routes terminated at the Missouri River, two thousand miles from the California goldfields. To get there by land, you had to traverse, by foot and wagon, the Great Plains, the Rocky Mountains, the deserts and salt flats—whose fatal aridity was soon evidenced by the discarded belongings and bleaching bones of earlier parties—and, finally, the sheer walls of the Sierras, which, no matter how exhausted and emaciated both man and beast were by then, had to be crossed before the snow started falling. All told, the journey generally took half a year. Nearly one in ten did not survive it.

The wonder is how many attempted it. In 1849 alone, more than forty thousand people travelled overland to California, while roughly the same number headed there by sea. This sometimes entailed sailing to Panama, crossing the jungled isthmus partly by canoe and partly by foot, horse, or mule, then waiting for another vessel on the Pacific side—a shorter journey, in theory, if the bottleneck wasn’t too bad and you didn’t succumb to malaria or yellow fever.

Alternatively, you could do what those Nantucketers had done and set sail from the East Coast, track southward all the way to Cape Horn, pass through the terrifying waters where the world’s two largest oceans meet, then head north again, clear around the hemisphere to San Francisco. That, too, took around six months, plus an iron stomach.

No matter the route, the duration of the journey was at drastic odds with its perceived urgency. Those who were obsessed with reaching the goldfields were maddened by the exigencies of getting there, and so, Philbrick writes, “a seething impatience gripped the American people that hasn’t let go of us yet.”What drove these California-bound migrants particularly crazy, he continues, was “the knowledge that tens of thousands of people are ” Some of these were long-standing residents; Native Americans had called the region home for millennia, and, in 1849, tens of thousands of them lived in the vicinity of the Mother Lode.

So did many Mexicans, known as Californios, who had lately been expatriated without moving an inch: California had been part of Mexico until 1848, when it was ceded to the United States at the end of the Mexican-American War.

But others were recent arrivals. Even Australians who wanted to get to San Francisco had less than half as far to travel as someone sailing from New York, and more than ten thousand of them soon passed through the Golden Gate. China was likewise comparatively proximate, and huge numbers of its people crossed the Pacific to reach the mines. Immigrants poured in from Latin America, too, especially Chileans, who hailed from a country rich in precious metals, and who taught many a New England lawyer and Midwestern farm boy the art of mining. Thirty thousand French people came to seek their fortunes as well; locals called them Keskadees, a corruption of “Qu’est-ce qu’il a dit?”—what did he say? Well might they ask.

The newly named city of San Francisco, which had been a sleepy port village with perhaps eight hundred residents in 1848, suddenly became a booming Tower of Babel. By 1849, property there had become some of the most expensive in the nation, even when it wasn’t desirable, or, for that matter, habitable; many people lived in tents, but there was also a thriving business in “water lots,” which were staked out in the bay to someday be filled with rubble and converted to land.

The streets, where they existed, were tunnels of wind-whipped dust in the dry season—one resident called it Sand Francisco—and a muddy mess the rest of the year. Out in the harbor, the skeletons of derelict ships abandoned by sailors who had gone searching for gold formed the first and strangest San Francisco skyline. And yet this inhospitable, half-built, helter-skelter city was, for a while, the destination of choice for profiteers, speculators, and schemers from every corner of the globe.

While California was becoming a magnet for those from abroad, it was provoking a political crisis at home. In 1849, there were thirty united states—fifteen of them slaveholding, fifteen of them free. Constantly rebalancing that map had been an unhappy necessity from the earliest days of the Republic, but the discovery of gold in the brand-new territory of California set off a national furor over what kind of state it would be.

Most histories of the Civil War divide the nation into North and South. Give or take Bleeding Kansas, most also focus their attention east of the Mississippi River. “The Rush” redraws that map, relocating the center of gravity westward, to California. As Philbrick makes clear, sectarian concerns over who would control the state’s wealth ran high from the beginning, and many of those who went West after 1848 were not just seeking a private fortune.

Instead, as would later happen in Kansas and Nebraska, slaveowners and Southern sympathizers on the one hand and abolitionists and Free-Soilers on the other all flocked to California to try to tip the political scales in their favor.

In this demographic competition, the South had both geography and weather on its side. Migrants from the slave states could head West at any time of the year, along a route known as the Gila Trail, which passed through New Mexico and Arizona to the southern edge of California. By contrast, those from the Northern states had to time their journeys carefully, since the Rockies and the Sierras could not be crossed in winter. In part because of this advantage, the South made steady inroads in the California interior, where town after town soon announced its cultural allegiance right on Main Street, via businesses like the Texas Saloon, the Mississippi Shoe Shop, and the Alabama Emporium.

Still, the North quickly established a strong presence in San Francisco, and it had something going for it in the goldfields, too: thanks to their work, many miners had a profound antipathy to forced labor. Philbrick tells the story of a Texan who showed up in a popular mining area and started staking claims not only for himself but also for his fifteen enslaved workers; in short order, he was run out by outraged locals. This resistance to slavery had little or nothing to do with humane fellow-feeling.

“Not one in ten cares a button for its abolition,” the then mayor of Monterey wrote, of the miners there. The real issue was that the presence of the enslaved in the gold mines increased the ranks of the competition.

In the end, of course, the opponents of slavery were victorious. When a group of delegates assembled to write a constitution for California, in the autumn of 1849, they unanimously agreed that, within its borders, “neither slavery, nor involuntary servitude, unless for the punishment of crimes, shall ever be tolerated.”A year later, via the Compromise of 1850, California officially became the Union’s thirty-first state and its sixteenth free one. But this triumph came at a considerable cost to the rest of the nation: in exchange, the South got a dramatically harsher Fugitive Slave Act, which stipulated that all American citizens could be required to help capture runaway slaves, and established heavy fines and prison sentences for those who aided fugitives.

Meanwhile, trouble was also brewing in California, where surface gold was getting harder to find and the competition for it was getting uglier. Gangs of armed Americans fanned local resentment of immigrants and steadily drove them off their claims and out of the country. A new law required Californios to prove the validity of their property titles in court, an expensive process that took an average of seventeen years; meanwhile, squatters made use of extrajudicial means, from burning crops to outright murder, to make them give up their increasingly valuable land.

But the worst fate befell the region’s Native Americans, who were first driven from the goldfields and then subjected to a campaign of wholesale annihilation. White militias destroyed their homes, torched their food supplies, and slaughtered them outright so routinely that a secondary economy of kidnappers sprang up to sell the survivors, children and adults alike, into servitude.

Philbrick relates all this less as history than as a stage play. He is fond of characters and good at depicting them, and he does not so much trace the influence of the gold rush on the Civil War as introduce us to various people with a stake in its outcome. One of these was William Gwin, a wealthy Mississippi plantation owner turned California power broker who was bent on aligning his new home with the slave states and making himself one of its first senators.

Another was David Broderick, a working-class Irish American politician from New York whose crew of henchmen belied his sensitive streak; he didn’t drink, never married, avoided brothels, spent his free time alone reading literature, and despised the institution of slavery.

Both Gwin and Broderick ultimately ended up in the Senate, and Philbrick describes the clash between them as “the center of the narrative” of his book. But that is not the reader’s experience, partly because “The Rush” is too desultory to have a center and partly because neither man stands out particularly clearly against the ensemble cast. This includes at least thirty-three major characters, some of whom are more memorable than the putative protagonists. The abolitionist Jessie Frémont, for instance, was married to the famous war hero John Frémont but was, as a contemporary observer commented, “the better man of the two.”

After John lost the 1856 Presidential election to James Buchanan, it was widely whispered, according to her obituary, “that if the lovely Jessie had been the actual candidate, she, and not Buchanan, would have occupied the Presidential chair.”Another star turn goes to Mary Ellen Pleasant, who was arguably America’s first Black millionaire and inarguably one of the most canny and chameleonlike figures this country has ever produced.

“I am a whole theatre unto myself,” she once declared, and it was true; she was, among many other things, an abolitionist, a civil-rights activist, a domestic worker, a domineering owner of boarding houses and laundries, and a supporter of John Brown, though Philbrick gives far too much credence to her claim to have been his most important financial backer.

It is a pleasure to meet these people in “The Rush,” but not every character makes an equally strong case for belonging there. Primary sources are a necessary and wonderful tool for historians, but they can have a fun-house-mirror effect, making some aspects of the past bulge and others narrow. To his credit, Philbrick is sensitive to those parts which we usually see inaccurately or not at all. He tells us, for example, that, although more than ten thousand Chinese workers helped build the transcontinental railroad, not a single diary or letter from one of them has ever been found, leaving a vast lacuna where their own California story should be.

Still, “The Rush” is ultimately more hamstrung by what it contains than by what it does not. We spend the first fifty pages of it following one Vicente Rosales, a Chilean man who arrived in California in early 1849. Rosales was a keen observer of life in and around the goldfields, but his experiences there, though interesting, don’t really bear on any of Philbrick’s broader themes. Yet we are spared no detail about him—down to the number of cows he brought home from a visit to Monterey and the day job of the man who once dug a well for him—and one suspects that Rosales earned his lengthy place in these pages not because his story was particularly relevant but because he documented it so thoroughly.

A similar problem of abundance attends the book over all. Philbrick has a keen eye and a magpie curiosity, and he can’t stop finding fascinating tidbits to share, from the 1850 flooding of the city of Sacramento to a brawl on the floor of the House that made thirty-seven members of Congress, many of them otherwise given to bloviating, forget the old dictum about using your words. All this is fun to read, since Philbrick is an adept and congenial storyteller. But well told is not the same as telling, and, in the end, the overarching claims in his book are occluded rather than revealed by the surfeit of detail.

Or perhaps the claims themselves are the problem. It is true, of course, that the discovery of gold in California altered the balance of the states and the economics of the nation, but Philbrick never mounts a convincing case that it was therefore decisive to the course and conclusion of the Civil War. Yes, the Compromise of 1850 played a role, but so did a series of political and constitutional crises that had little or nothing to do with California and its gold, including the Missouri Compromise, the Kansas-Nebraska Act, the Dred Scott decision, and the election of Abraham Lincoln.

To support the claim that California’s enormous wealth helped win the war, Philbrick quotes Ulysses S. Grant saying, while the battles were still raging, that he did not know what the North would do “if it were not for the gold sent from California.”That’s interesting but hardly probative, and countless other factors, unmentioned by Philbrick, contributed to the stronger financial position of the North, such as greater banking and borrowing power and a more industrialized economy and a larger population.

Philbrick himself, having set out to write about the gold rush and the Civil War, nonetheless seems tentative about the relationship between the two, and the one he establishes is not so much causal as metaphorical. “The discovery of gold in California,” he writes, “was part of a much larger—and ultimately more consequential—rush: the rush to the Civil War.”Yet even the metaphor stumbles, since it is hard to see anything like the mad frenzy of the forty-niners in the very long road to the Civil War, whose origins date all the way back to the founding of the United States.

How much explanatory work can—or should—a single word do? From the title on down, “The Rush” makes much of the idea of rushing, of the allure and danger of speed and impulsivity. Indeed, that idea becomes the book’s organizing principle; it explains why we skip over most of the Civil War itself, which cannot be contained within that rubric, but spend fifty pages on the construction of the transcontinental railroad, a way to hasten the movement of people and capital across the country.

And it explains, too, the otherwise odd finale of “The Rush,” which concerns the photographer Eadweard Muybridge. In 1860, Muybridge was thrown from a carriage, resulting in a head injury that radically changed his personality and possibly heightened his artistic inclinations. The accident took place in what is now southeast Oklahoma, and Muybridge, headed for Europe, was planning to put a whole ocean between himself and the goldfields, yet Philbrick writes that “Muybridge had been brain-damaged by the Rush.”

That strains credulity, but the larger question is what Muybridge is doing in this book in the first place, other than famously taking mid-gallop pictures of a horse belonging to Leland Stanford—the former governor of California and the owner of a sprawling estate south of San Francisco that he named for an exceptionally tall redwood tree nearby. The answer is that Muybridge helps form the dots Philbrick wants to connect for us by way of conclusion: the invention of motion pictures (“the Rush could now be projected onto a screen through a gas-lit device Muybridge called the Zoopraxiscope”), the origins of Palo Alto (meaning “tall tree”), and the founding of Stanford University, “the nucleus of what we now call Silicon Valley,” which “spawned one technological ‘gold rush’ after another—the microprocessor, the microcomputer, the internet, and artificial intelligence.”Like so many of us, Philbrick is gravely worried about the latter: “We are all passengers on a hurtling train. The end of humanity might be the ultimate destination.”

In Philbrick’s framing, the root cause of this crisis was the discovery of gold in California nearly two centuries ago. “This is the world in which we live today,” he writes earlier in the book, “jammed into jets on our frantic way to the next new thing—a world created in 1849 by the California Gold Rush.”But did the gold rush create our contemporary world, or do the two just resemble each other?

It’s true that many features of eighteen-fifties California are also visible in the current A.I. boom, from the benefits of arriving early and the outlandish profit to be made in infrastructure—whether picks and shovels or microchips and data centers—to political instability, environmental destruction, and wild inequality. But resemblance is just a surface relationship, and nothing in Philbrick’s book makes the gold rush seem like a motive force behind the breakneck, and maybe break-everything, boom of today.

Nor does anything in it make avaricious urgency seem specifically American; how could it be, when all those Aussies and Frenchmen and Chinese and Chileans likewise dropped everything and sped to California?

The more plausible explanation is this: put any group of people within striking distance of a potential source of spectacular wealth, and many of them will behave in similar ways, including moving toward it, competing for it, cheating over it, exaggerating about it, inventing new ways to extract it, creating rules to manage access to it, breaking those rules, and generally using all available means, legal and otherwise, to dominate and profit from it. “The Rush” is at its best when it simply shows us this mayhem as it unfolded in a specific place and period, instigated, abetted, opposed, documented, and occasionally averted by marvellously specific human beings.

One sympathizes, in these dark and confusing times, with the desire for the past to illuminate the present. But the past is its own kind of gold—abundant, difficult to access, inordinately valuable—and sometimes it is enough to let it shine.