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Photographer: Barry Swackhamer
Taken: March 14, 2013
Caption: Geological Interpretive Panel
Additional Description: A Trip to the Beach

Close your eyes and listen very carefully. Can you hear the sound of ocean waves crashing on the shore? It’s hard to believe, but the land that is now Alum Rock Park was once a beach with an ocean view. The rocks and minerals found throughout the park can tell us how things have changed from an ocean beach to the beautiful canyon you see today.

The sandstone rocks filled with fossilized sea shells found near here help to tell the story. About 15 million years ago, this area was flat, sandy beach. Over thousands of years, layers of mud, sand, and silt settled to the ocean floor. Pressure and time caused the layers to form sedimentary rocks such as sandstone and shale. Earthquakes and volcanic activity pushed these layers into folds and ripples, helping to create the hill and mountains and push this area away from the ocean. You can clearly see layered rocks pushed and even folded into may beautiful curves on the surrounding hillsides. The flowing waters of Penitencia Creek have cut through these layers creating the deep, narrow canyon that is now Alum Rock Park.

The Mineral Springs

All of this ground-shaking activity has created an abundance of natural mineral springs in the park. The spaces between the layers of rock form tiny pipelines that water can flow through. Rainfall onto the mountain above the park seeps into these tiny pipelines. Over hundreds of thousands of years, the water creeps slowly through these pipelines until it finds an opening to flow out of. By the time the water reaches an opening, it has been warmed by the earth and has picked up traces of minerals. Geologists studying Alum Rock Park have discovered over 20 different mineral springs. Sulfur, magnesia, iron, natural soda, and even carbonated springs can all be found nearby.

Alum Rock Park Interpretive Series
San Jose Parks, Recreation and Neighborhood Service
Submitted: March 17, 2013, by Barry Swackhamer of Brentwood, California.
Database Locator Identification Number: p236396
File Size: 3.269 Megabytes

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