Twisted and colored over time
Site: Devil’s Punchbowl
Where: Devil’s Punchbowl County Park,
Pearblossom
Written in stone: Devil’s Punchbowl County Park is a hidden gem of northern Los Angeles County, and it’s all about the rocks. The Punchbowl Formation is spectacularly exposed in a deeply eroded cistern just south of the San Andreas fault.
The pinkish rocks of the Punchbowl contain sand, pebbles and cobbles similar to those that score the San Gabriel Mountains in the background. Fossilized mammal bones from the Punchbowl suggest that the rocks were horizontal during the Pliocene era, as much as 5 million years ago, but have been tilted by tectonic activity along the San Andreas fault, just to the north. They subsequently were eroded into a fantastically jumbled landscape.
The Punchbowl materials were originally deposited on ancient alluvial fans, similar to the debris washed out of the mountains by this year’s phenomenal crop of landslides and floods. But a key difference is that the Punchbowl debris probably came from the east and northeast, not from the south or west.
A few sparse maroon bands of mudstone interlayered with the sand and gravel are the product of ancient soils that collected on the fans between the debris flow events.
-- W. Britt Leatham
Biostratigrapher,
Cal State San Bernardino
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