The white Toyota Tacoma bumped along the dirt path, up and down hills, brush scratching the sides of the truck with a high-pitched whine. Naomi Fraga, her hair in pigtail braids under a ball cap, drove like a slightly more cautious Indiana Jones guided by an ancient map.

She stopped the vehicle on a perch overlooking an expanse of boulders and Joshua trees in eastern Kern County, about 170 miles northeast of Los Angeles.

“This is right where they’re supposed to be,” she said.

Dr. Fraga, 43, was on a treasure hunt, but not for gold or jewels. She was scouring the desert for delicate blooms so tiny that they are called “belly flowers,” because botanists must get down on their stomachs to get a proper look at them.

This winter’s relentless rain produced a bounty of flowers across California this spring, delighting residents with vibrant color in places like the Antelope Valley California Poppy Reserve, where visitors have lined up to take selfies with the displays. After unusually wet spells like this, species emerge that haven’t been seen in years.

To Dr. Fraga, a botanist with the nonprofit California Botanic Garden in Claremont, this spring affords an extraordinary opportunity to document the existence of rare plant species so that they might be saved from the brink of extinction.

This swath of Central California, where the Sierra Nevada mountains blur into the Mojave Desert, was once part of a vast, untouched landscape. Billions of microscopic seeds lay dormant in the top layer of earth for years, even decades, until conditions were exactly right for them to emerge as wildflowers.

Historically, spring has been marked by a dazzling variety of flowers across the West, each suited for its particular environment. (California, one of the most biodiverse places on the planet, is home to at least 2,400 rare plant species.)

Over time, farms, homes, and off-road vehicles have chipped away at patches of rare-plant habitat — a hillside here, a meadow there. Climate change has shifted when, where and how much it rains. Even in places where carpets of wildflowers still bloom in wet years, crowds can imperil their future.

So this spring and summer, Dr. Fraga and other rare-plant biologists are in an exhilarating race to find wildflowers before they disappear again.

The botanists’ ultimate goal is to secure endangered or rare species designations for the most threatened plants. That can lay the foundation to legally force land managers to make accommodations for threatened species. (For instance, the Center for Biological Diversity has made wildflower protection a key piece of its lengthy fight against development of the Tejon Ranch, where almost 20,000 new homes have been proposed north of Los Angeles.)

In order to get endangered or rare species designations, Dr. Fraga and her colleagues must first prove that the plants still exist. Dr. Fraga may be the only person equipped to do that for the plants she studies, said Katie Heineman, a vice president of the Center for Plant Conservation.

“Without her, there would be no knowledge of that plant species in the entire world,” she said. “It’s what drives conservation action: Having people who are fully trained looking at these plants in the field.”

On this trip, Dr. Fraga was looking for a species known as the Kelso Creek monkeyflower, with blossoms half golden yellow and half rich maroon.

“We each have our pet species,” Dr. Fraga said. “I just wish we could do more. We keep talking about the extinction crisis, but we only know if things are going extinct if you keep track of them.”

Dr. Fraga sees the broad acceptance of habitat destruction in California as a kind of slippery slope. Each flower represents millenniums of evolution. If we accept the extinction of one obscure monkeyflower, she worries, where might it end? And what consequences might there be for disrupting complex ecosystems?

Each spring, Dr. Fraga and her fellow conservationists, including amateur botany enthusiasts who use apps like iNaturalist, try to document as many rare plant populations as they can.

Scientists must meticulously plan to find targets in peak bloom. If they arrive at a location hours too early, the flowers might still be ensconced in their buds, making them harder to study. If they arrive too late, the flowers may have already shriveled in the heat.

Dr. Fraga homed in on monkeyflowers after stumbling upon a science career she never thought she’d have.

Her father, a Mexican immigrant who worked as a truck driver, thought she should become a kindergarten teacher after she was the first in her family to attend college. But at age 20, a mentor — also a Mexican American woman — took her on her first hike, to hunt for a rare herb. Her feet ached from her ill-fitting boots, but she was hooked. Dr. Fraga later felt the thrill of discovery; she has found five new species of monkeyflower.

As a Latina, Dr. Fraga is a trailblazer in a field long dominated by white men, dating to the 1700s when European colonists traveled the world and built collections of exotic plant specimens, many of which are used by scientists today. (The oldest specimen in the California Botanic Garden’s collection dates to 1750.)

“It’s a complicated legacy,” she said, pausing near a patch of purple owl’s clover, a native wildflower.

Later on the trail, Dr. Fraga scanned clusters of butter-colored desert dandelion and scale bud, and hustled past lines of pale cream cups. Insects buzzed and lizards darted across her path.

She stopped suddenly. “Oh my god! A hybrid!” she cried.

A Kelso Creek monkeyflower had somehow crossed with a rock jasmine monkeyflower, another close species. She had never seen one in person before. She stopped to photograph the plant and take detailed notes about its features.

“Actually, you’re coming with me,” she said, after spotting another one. She carried the plant back to the truck, where she pressed it between pages of the Claremont Courier.

But the Kelso Creek monkeyflower, her target for the day, was still proving elusive. She frowned, perplexed. “This is good habitat,” she said.

She met up nearby with three of her students, and the group consolidated into two trucks. They splashed through the khaki-tinted Kelso Creek, for which the flowers are named, to check one more location where Dr. Fraga had seen a small bloom of a few hundred plants the year before.

Across the creek, they saw a field that, from afar, looked like green scrub and cactuses. But as they approached, the botanists gazed in astonishment: a sea of petite plants with yellow and maroon flowers rolled ahead. There were millions, the group estimated later.

“It’s a micro-super bloom!” gasped Courtney Matzke, 35, one of the students.

They had finally found their flowers. The afternoon sun bore down.

It was time for Dr. Fraga and her students to get to work.