From thick, black mud came treasures — fishhooks; stone tools; snail shells; fish, bird and animal bones; petrified leaves, seeds and insects; and wooden gourd stoppers, tattoo needles and parts of canoes and paddles that revealed what life was like on Kauai as far back as 400,000 years ago.

Excavations at Makauwahi led by Dr. David Burney and his wife, Lida, have yielded millions of fossils and artifacts, making it arguably the most valuable archaeological find in the Pacific.

Many local people already knew about the sinkhole and cave system connected to it when the couple came across it 27 years ago. What they literally brought to light was the valuable cache that had long been hidden in the sediment there.

In August 1992, the Burneys were enjoying a Kauai vacation with their children and friends Storrs Olson and Helen James (Smithsonian Institution researchers at the time) and their kids. While on an afternoon walk with his son Alec and James, Burney noticed fresh footprints going into a thicket.

Curiosity piqued, the trio followed them to a hole at the foot of a cliff that was just big enough for them to crawl through. Emerging in a half-acre sinkhole, they saw two caves at ground level, but overgrowth and waning light prevented them from exploring further.

The next morning, they returned to Makauwahi with the rest of the group and a small auger to get a few core samples. The first yielded three species of extinct land snails; the second, the skull of a small bird.

To the globe-trotting Burney, known for his work in paleontology and ecological history, it was like a miner striking gold.

Initial studies of the 17-acre site began in 1992; full-scale excavations launched in 1997. Three other caves were later discovered higher up on the sinkhole’s walls and three more below the water table.

Burney has described conditions at Makauwahi as the “Goldilocks zone — just right”; the alkaline in its limestone walls offset the acid in the groundwater to create the perfect pH balance for preservation of fragile, prehistoric specimens.

“An acidic environment would have disintegrated bones, and plant fossils would not have survived in an alkaline environment,” he said. “But in a neutral environment, everything has been well preserved in layers as deep as 33 feet below the sinkhole’s floor.”

In 2004, the Burneys obtained a lease for Makauwahi from owner Grove Farm Company and established the nonprofit Makauwahi Cave Reserve (MCR) to ensure proper stewardship of it. Grove Farm subsequently made about 100 acres of surrounding wetlands and abandoned quarry and agricultural land available for reforestation.

The arrival of Polynesian and European settlers, the plants and animals they brought and the ensuing cultivation and development triggered the demise of many native species in Hawaii. Based on fossils their archaeological digs spanning two decades uncovered, the Burneys launched efforts to restore the ancient ecosystem. To date, invasive introduced vegetation has been removed from 25 acres, enabling native shrubs, flowers and trees to be reestablished (see sidebar).

Strolling in the sinkhole today — with sunlight streaming in from the sky-ceiling and surrounded by multicolored, multilayered limestone walls rising 30 to 80 feet — visitors learn secrets that were buried in sludge for thousands of years. For instance, the remains of more than 40 bird species have been recovered at Makauwahi. Most of them are now extinct, among them flightless ducks and geese.

Also of note is Pritchardia aylmer-robinsonii, which is endemic to Niihau and recognized as one of the rarest palms in the world. Seeds for the Pritchardia aylmer-robinsonii flourishing in restorations throughout the reserve came from the few trees that remain in the wild.

“We chose that species because its unique spherical-shaped seeds matched about 95% of the fossilized palm seeds we found in the sinkhole,” Burney said. “That means it was once abundant there; why, then, did it disappear? Rats that came to Hawaii as stowaways on Polynesians’ canoes ate the palm’s seeds before they could drop to the ground and sprout. People probably also contributed to its decline by overusing its leaves for thatch.”

Previously, scholars could only imagine what Kauai was like before humans arrived. The work at Makauwahi has provided them with a much clearer picture of what greenery existed and what can be restored.

“We can’t bring back the species that have been lost, but, moving forward, we now have a map to follow,” Burney said. “From a geological and archaeological point of view, Makauwahi is a gem. When you’re there, it’s like you’ve entered a time warp — whisked back thousands of years to a primordial refuge. It’s an amazing living classroom, and it’s accessible. There’s no other place in Hawaii like it and few like it anywhere in the world.”

The work continues

Several restoration projects have been guided and inspired by the archaeological discoveries at Makauwahi. Among them:

>> In 2004, an adjacent abandoned sugar cane field was a tangle of invasive, non-native plants. Volunteers and Kauai schoolchildren cleared and plowed the field, then planted hundreds of native dry forest trees, shrubs, ground covers and Polynesian food plants to re-create the type of vegetation that would have existed 1,000 years ago.

>> Started in 2012, another project has transformed a second abandoned cane field into 15 “pond fields” planted in taro and other native wetland plants. Old maps, oral history and archaeological finds indicate that Hawaiians farmed wetlands there for centuries.

The newly created wetlands have been colonized by native waterbirds, including four endangered species found only in the Hawaii: alae ula (Hawaiian moorhen), aeo (Hawaiian stilt), koloa maoli (Koloa duck) and nene (Hawaiian goose, Hawaii’s state bird). Fossils of these birds prove they have thrived in the area for thousands of years.

Giant tortoises wander through fenced habitats near the sinkhole, fertilizing the soil with their feces and helping to control invasive weeds and grasses. Although they’re not native to Hawaii, the tortoises’ role is similar to the herbivores, including large flightless waterfowl, that were once abundant in Hawaii.

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Adapted from wayside exhibits produced by the Makauwahi Cave Reserve

Cheryl Chee Tsutsumi is a Honolulu-based freelance writer whose travel features for the Star-Advertiser have won several Society of American Travel Writers awards.