In November 1849, eight men set out from their “gold diggings” on the North Fork Trinity River in Northern California into a range of forested mountains that had never been mapped. Their leader was Josiah Gregg, a math whiz, self-taught navigator, medical doctor, and obsessive botanist. The Indians they’d met along the North Fork had described a large, sheltered bay on the Pacific shore, an eight-day walk to the west. Such a bay could make them all rich — if they got there before other settlers, they could lay claim to property and exploit the inevitable flood of miners eager to follow a new route to the gold-rich Trinity.

WHAT I LEFT OUT is a recurring feature in which book authors are invited to share anecdotes and narratives that, for whatever reason, did not make it into their final manuscripts. In this installment, author Sharon Levy shares a story that didn’t make it into her latest book “The Marsh Builders: The Fight for Clean Water, Wetlands, and Wildlife,” (Oxford University Press.)

Two Indians had offered to guide the party through the mountains, but by November 5, the date Gregg had set for the expedition to start, a steady snowfall had cloaked the mountain summits in deep drifts. The Indians refused to go and warned Gregg that snow made the route deadly. Of the 24 men who’d volunteered, all but seven turned away. Gregg and his seven die-hards began to climb west, up a trackless mountain.

“Here commenced an expedition, the marked and prominent features of which were constant and unmitigated toil, hardship, privation, and suffering,” wrote Lewis Keysor Wood, who would be maimed by grizzlies during the journey but survive to become a founding father of the city of Arcata, on Humboldt Bay. The crossing took weeks instead of days, and for much of the time, the explorers had no food to eat. They toiled west in snow and rain, without tents or dry clothes.

All this made the men irritable — and their leader, Gregg, could be a very irritating man. At 43, he was two decades older than most of the other members of the expedition. He possessed some remarkable talents, but relating to his fellow humans and boosting their morale was not one of them.

Gregg had a passion for measurement and for the clunky 19th-century tools that made it possible. As a boy, he built himself a wooden quadrant that he used to measure the heights of trees near his home on the Missouri frontier. The other kids tested his calculations by climbing up the trees with a measuring rope and were amazed at his accuracy.

As a teen, he taught himself surveying. Later, he hoped to apprentice himself to a physician, but he was refused because the doctor thought Gregg too frail. By 1830, Gregg was 24 years old and seriously ill. When other treatments failed, his doctor prescribed a trip across the plains with a wagon train heading to Santa Fe. It was a rugged, thousand-mile journey that would take about 10 weeks.

Gregg began the trip as a feeble passenger, lying in a wagon. Within a few days, he was well enough to saddle his pony and ride for part of the day. Soon, he was eagerly hunting buffalo. The hazard and adventure of the plains restored Gregg’s health and gave him reason to wield his compass and sextant, a navigational instrument he used to measure latitudes and map routes. He would spend the next nine years as a Santa Fe trader, recording the details of his travel in a meticulous journal, relishing his encounters with Comanche raiders. It was his peak experience. After leaving the plains in 1840, he wrote a best-selling account of his years there.

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He was happy and relatively healthy on the trail; in civilization, he was often ill, suffering from painful sinus and gut problems. When he felt rotten, he wrote to his brother John that he was “unusually crabid.”

Gregg always followed his obsessions. In 1845 and 1846, he at last attended medical school, where he befriended fellow doctors who were also skilled botanists. He became fixated on plant collection, gathering and preserving specimens from his travels in the Southwest and Mexico. Forty-seven plants from the region now carry the species name greggii in his honor.

Acting as a guide and interpreter for American troops during the Mexican War, Gregg recorded the bloody and decisive battle of Buena Vista in great detail. He collected plants on the battlefield, including Ceanothus greggii, a shrub with delicate and fragrant white blossoms.

He told others that he “had no desire to be considered an odd fish,” but that is how he often came off. While traveling in Mexico during the war, Gregg rode up to join an Army column on his mule, sitting stiffly upright and holding a red silk parasol. He and his mule were draped with plant presses, a sextant, and a daguerreotype machine. The soldiers found him ridiculous, and they let him know it. Gregg was dead serious about everything he did, which intensified the mockery.

At the height of the California Gold Rush, Gregg sailed from Mazatlán, a city on Mexico’s Pacific Coast, to San Francisco, arriving in September of 1849. He soon heard of rich new diggings on the Trinity River, as well as rumors of a navigable bay to the west, which had been visited by Spanish sailors decades earlier. He even found a record of the bay’s latitude. He headed to the Trinity with his sextant, compass, and botanical gear. “The Old Doctor,” as the miners on the Trinity would call him, was yearning for the exploration, mapping, and measurement that had marked his happiest years on the Santa Fe trail.

On the first day of their journey, Gregg and his companions struggled up a steep, trackless mountain. As they climbed, snow covered the slippery mud. They reached the summit, where they ate pork and beans from a can before wrapping themselves up in thin blankets to sleep on the snow.

The rag-tag group, later to be known as the Gregg Expedition, was attempting to move straight west across a mountain range whose ridges run north to south, parallel to the coast they hoped to reach. This meant they struggled up one steep mountainside, panted for a while on the summit, scrambled down into a deep wet canyon, and then started the process over again. It rained nonstop, and the men had soon finished off all the provisions they’d thought would last until they reached the Pacific. Gregg insisted on stopping to take compass readings and calculate latitudes. The other men loathed his scientific fussing and cursed him for it.

On the fifth day of their ordeal, they crossed a roaring stream, the South Fork Trinity River. On the opposite side, they walked into an Indian village, where the entire population scattered in panic at the sight of them. The hungry men raided the village stores of smoked salmon, loaded the food on their mules, and moved on. Soon the stolen salmon had been devoured, and the men were reduced to eating the moldy crusts that lined their empty flour sacks.

Relief came only when they stumbled onto mountain meadows, places that had been burned by native people for millennia to create openings in the forest. Elk and deer were abundant in these oases of grass, and the men were able to load up on venison, while their starving mules fed and recovered.

Weeks into the journey, they reached the redwood forest. Everywhere lay the massive trunks of fallen trees piled on top of each other. The men used axes to carve steps in the logs so the mules could climb up. Every member of the party, man or mule, was exhausted and starved; they were lucky to cover two miles a day. The mules began to die off.

In this extreme situation, Gregg’s obsession with measurement endured. He wanted to read the dimensions of the giant trees, a maneuver that required more than one person. “Not being in the most amiable state of mind and feeling at this time,” wrote Wood, “and having neither ambition to gratify nor desire to enlighten the curious world, we not infrequently answered his calls with shameful abuse.”

Gregg did manage to measure a few of the great redwoods, recording diameters up to 22 feet and heights of 300 feet.

When the party emerged from the redwood maze onto the open beach, they’d had nothing to eat for two days. One man managed to shoot a bald eagle, while another killed a raven feeding on a fish. That night, they stewed the eagle, the raven, and the fish in one pot.

The men were disgusted with Gregg, with his rigidity and his measurements, and his hunt for a navigable bay. They wanted only to return to civilization as soon as possible, and turned south, toward San Francisco.

At one major river crossing, Gregg stopped to read the latitude but the men refused to wait. They loaded themselves into redwood canoes borrowed from the local Indians and pushed off. Gregg was forced to wade into the river in pursuit, carrying his sextant.

On the other side, Gregg “opened upon us a perfect battery of the most withering and violent abuse,” Wood remembered. Some of the men discussed drowning Gregg and his scientific instruments in the stream, which was named the Mad River in memory of Gregg’s outburst. Soon after, they at last stumbled across Humboldt Bay, the waterway they had suffered so much to find. A native Wiyot leader named Kiwelatah fed them a sumptuous feast of clams, a kindness Wood would remember for the rest of his life.

As the expedition struggled south, the party split in two. Wood parted ways with Gregg.

Light-headed with hunger, Wood and his men tried to hunt a group of eight grizzlies. One bear grabbed Wood’s ankle, another his shoulder, and the beasts played tug-of-war with him, dislocating his hip. Unable to walk, Wood expected to be left to die. His comrades managed to pack him out on one of their remaining mules, a process that proved excruciatingly painful.

Out of ammunition and surviving on roasted acorns, Gregg’s group found the coast impassable and turned inland. Gregg fell from his horse near Clear Lake, and died in a few hours, without speaking. He was buried in a shallow, unmarked grave; his notebooks and instruments vanished. One historian speculated that Gregg may have suffered a stroke, or perhaps been murdered by desperate men who could tolerate his eccentricities no more.

The seven survivors of the expedition straggled back to American settlements. San Francisco newspapers soon carried word of the discovery of a wide bay — a suitable harbor for ships — on California’s far north coast. Multiple parties of aspiring miners and merchants immediately sailed for Humboldt Bay.

Wood returned to live on the bay, building a ranch he named Kiwelatah, and he wrote with regret of the brutal way his fellow settlers treated the native people. As for Gregg, who had been truly happy only on frontiers, he died exploring California’s last undisturbed landscape, opening it to a violent rush of settlement.

Sharon Levy spent a decade working as a field biologist in the woods of Northern California before taking up science writing full time. In addition to “The Marsh Builders,” she is the author of “Once and Future Giants: What Ice Age Extinctions Tell Us About the Fate of Earth’s Largest Animals.” She’s written for Nature, New Scientist, BioScience, and Undark, among other outlets.