Burnt Scallops and Fossil Fish: The Woolsey Fire and Santa Monica Mountains Fossils

Parks such as Petrified Forest and Dinosaur National Monument are famous for fossils, and big parks like Yellowstone, Grand Teton and Grand Canyon hold many fossil sites too. But one little-heralded unit stands out for sheer number of documented fossil sites: Santa Monica Mountains National Recreation Area (SAMO), on the Pacific coast of southern California.

The park

• Established in 1978, just west of Los Angeles, to protect natural and cultural resources from spreading development.
• The NPS administers it, but inside its boundary is a mosaic of federal, state, county and city lands and private property — rugged highlands, steep canyons, chaparral, coastal wetlands and beaches.
• It includes old filming ranches: Paramount Ranch (Gunsmoke, Westworld) and Century Ranch (Planet of the Apes, the M.A.S.H. TV series), chosen for landscapes shaped by a complicated, jumbled geologic history.

Nearly a thousand fossil sites

Close to Los Angeles, its county museum and many university geology departments, the eastern and central Santa Monica Mountains were combed by scientists and collectors for decades, producing nearly a thousand fossil sites — making SAMO one of the most fossil-rich units in the National Park System.

An early Miocene volcanic event, recorded in the Conejo Volcanics, helped shape the park's distinctive landscape.

The Woolsey Fire

Most known fossil sites were in the east and center, which were easier to reach; the west had only a few, mostly from Thomas Dibblee's geologic surveys. Then, in November 2018, the Woolsey Fire burned 96,949 acres — including 88% of the federal parkland in SAMO — and destroyed the park's collection facility and much of Paramount Ranch. Park staff asked for an assessment of the damage to fossils, which was also a chance to look for new sites in the west.

The survey ran in two parts: May 16–26 and December 4–14, 2023, with much credit to SAMO's natural and cultural resources staff.

Charbroiled scallops. On the first day, along the Zuma Ridge Motorway, botanist Mark Mendelson's vegetation crew spotted marine sandstones of the Vaqueros Formation full of large scallops and gastropods. Following the ridge down, the damage grew step by step:

1. sandstone tinged pink, and normally whitish shells turned bluish gray;
2. scorched, sooty edges and darker shells;
3. shell beds essentially charcoaled;
4. on the opposite ridge, shells burned away entirely, leaving only their impressions.

It was the first evidence that the fire had destroyed or altered fossils. In all, the survey found six sites with minor to severe damage to these non-renewable resources. Five years of erosion and regrowth — sped by a historically wet winter — had probably erased much of the evidence, so the full loss may never be known.

A silver lining: new sites, and fish at Paramount Ranch

Much of the burned federal land had barely been explored for fossils. The survey recorded 155 new fossil localities in the park's west and north.

The Calabasas Formation was the standout. Previously known for tiny fossils — foraminifera, diatoms, plant fragments, reworked mollusks and fish scales — it yielded, at two sites, partial to nearly complete fish skeletons, a first for this formation. They may show how fish communities changed from shallow offshore waters to the deeper habitats of the younger Modelo Formation.

One of those sites is at Paramount Ranch. For years its western-town film set stood — until the fire destroyed all but a few buildings — without anyone knowing that the ground underfoot had once been an ocean floor rich in fossils. The team also collected samples that they hope will seed a new fossil collection for SAMO and spark new research, showing that surveys after a disaster can still expand what a park is known to hold.

Sources

Based on "Burnt Scallops and Fish Fossils on Filmsets: Assessment of the 2018 Woolsey Fire on Paleontological Resources at Santa Monica Mountain National Recreation Area," by John-Paul Hodnett (National Park Service Paleontology Program and M-NCPPC Dinosaur Park), Park Paleontology News, Spring 2024, National Park Service; rewritten in hubnx's own words. The source spells the formation both "Vaqueros" and "Vaquero."