At this EarthCache, you will explore the sandstone of Stoney Point Park, part of the Chatsworth Formation. The two waypoints are close together. At the first, you will compare a weathered outcrop with a roadcut. At the second, you will look closely at the rock itself.
There is parking on the east side of Topanga Canyon Blvd toward the 118 Freeway. Use caution, traffic is fast.
Geologic Background
Stoney Point sandstone formed more than 65 million years ago from turbidity currents, which are underwater slides of sand and silt. When the current slows, coarse grains settle first, then finer ones, creating layers that become rock. Over time, these layers hardened into sandstone and were lifted to the surface.
You may see:
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Layers or bands from multiple events
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Grains that get finer upward (graded bedding)
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Ripple marks or cross lines
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Rounded, gritty sand grains
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Pits from weathering and erosion
Waypoint #1 – Park Sign
Look at the large sandstone outcrop in front of you.
Then look across the road to the 1963 freeway roadcut.
Task 1: Compare the two. What differences do you see in color, texture, or weathering?
Waypoint #2 – Close Sandstone
Walk a short distance to the second waypoint. Use an unpainted rock.
Look closely at the rock’s surface.
Task 2: Describe the color, texture, and layering. What does this tell you about how it formed?
Task 3 – Rock Climbing
Stoney Point is a popular climbing site.
Question: Why do you think this sandstone is good for climbing?
Logging Requirements
Visit both waypoints.
Send me a message with your answers to Tasks 1–3.
Photos are optional but must not give away answers.
Sources