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In 1993, scientists charting the Pecho Coast Trail stumbled upon a startling discovery

I believe that one of the most beautiful hiking trails found anywhere along the Central Coast is the Pecho Coast Trail, which is guided by knowledgeable docents and leads to beautifully restored Point San Luis Lighthouse. This light station has thrown a welcoming beam of light out to sea since 1890.

If you travel farther along the trail, pass the lighthouse and head northwestward for a few miles along the 85-foot-high coastal terrace, you’ll reach Rattlesnake Canyon, where a historic discovery was made in the spring of 1993 due to a very wet year.

The rain season of 1992-93 produced over 31 inches of precipitation. In January and February, nearly 15 inches of rain was recorded at the Diablo Canyon Ocean Lab, and the ephemeral springs and creeks flowed fiercely, dumping brown and gray sediment into the Pacific along the coastline of San Luis Obispo and Santa Barbara counties.

In the summer after the creek beds turned dry, I remember exploring a few of these crevasses looking for attractive rocks exposed by the water’s erosion.

In the late spring of 1993, when PG&E was developing the Pecho Coast Trail, a PG&E biologist and archaeologist, Cal Poly’s paleontologist, and a few folks from the Nature Conservancy discovered a curious rock with deep ridges in the dry creek bed at the bottom of Rattlesnake Canyon.

Upon further investigation, it turns out it was a gigantic tooth, but from what?

It was collected by Dr. Harry Fierstine of Cal Poly, and to his amazement, it was determined to be a Columbian mammoth molar dated to be between 12,000 and 80,000 years old. These ridged teeth were used to grind grasses and woody vegetation. Columbian mammoths most likely spent most of their day eating hundreds of pounds of food.

The woolly and Columbian mammoths were quite different in appearance as the more massive Columbian mammoths thrived in the temperate savannas to the south, and the smaller Woolly mammoths thrived in the cold steppes of the north. The Columbian had large tusks and not much fur.

Not only were remains from a Columbian mammoth found, but also a toe bone from a prehistoric giant ground sloth that weighed as much as 2,000 pounds. When this mammoth of Rattlesnake Canyon was alive, sea level was as much as 120 feet lower than today due to the immense amount of frozen water locked in gigantic ice sheets in the far northern and southern latitudes during the Ice Age.

During this time, the jet stream or storm track, which brings precipitation from the Pacific Ocean, was primarily centered over California and the American Southwest. Sedimentation samples indicate that average rainfall amounts were much higher than today.

“During the last ice age, there is evidence along our coast that over 10,000 years ago, there was a wetter climate and an abundance of grasslands and green vegetation. Enough vegetation for Columbian mammoths to thrive along our coastline. It was more massive than the modern African elephant and stood 13-feet high at the shoulders, its head as high as 16 feet. They weighed as much as 20,000 pounds or as much as four pickup trucks,” retired PG&E biologist Sally Krenn said.

Krenn told me, “At the end of the Ice Age, the amount of rain along the Central Coast decreased, causing a loss of habitat and at the same time, humans invaded North America, hunting mammoths for food. Both of these events caused the Columbian mammoth to go extinct around between 10 and 13,000 years ago.”

The molar was given to the Los Angeles County Museum of Natural History, but two casts were donated, one for PG&E that is on display at the PG&E Energy Education Center and the other to The Land Conservancy of SLO. PG&E and The Land Conservancy both encourage volunteers to get involved with their programs as one can learn to share the beauty and history with others.

“PG&E trains volunteers to lead hikes on the Pecho Coast trail, which encourages an understanding, appreciation and protection of the human and natural history of this diverse environment. Docents serve as ambassadors to the public, fostering the further development of the conservation community,” said PG&E terrestrial biologist, Kelly Kephart.

If you are interested in becoming a docent for the Pecho Coast Trail (call Leon at 805-528-8758). If would like to hike this incredible trail, please visit PG&E’s Diablo Canyon hiking trails page at for more information.

Learning Among the Oaks (LATO) is The Land Conservancy’s innovative outdoor learning and youth environmental leadership program. LATO connects kids with nature, fosters lifelong learning skills, and inspires tomorrow’s conservation leaders. The mammoth molar is a teaching tool for the LATO “Animals and Oaks Through Time” hike curriculum developed in collaboration with Cal Poly Senior Project students. If you are interested in volunteering for the LATO program, Contact LATO Program Director Alex Zewiski at

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