Logging Requirements
To log this EarthCache, visit the posted coordinates at the central canyon floor and answer the following questions based on your on-site observations. Please send your responses before logging your find to me via the Geocaching message center or email. And as always, please be respectful of the natural features while you're exploring.
At the posted coordinates, face west and focus on one of the nearest exposed canyon walls with cross-bedding to answer the following:
- Look closely at one spot on the rock wall. Describe the slanted layers you see there. Include the direction they lean, how thick or thin the layers are, and the colors you notice.
- Notice how steep the slanted layers are. Do they tilt gently or sharply? What might this tell you about how fast the water or wind was moving when these layers formed?
- Now look across the rock wall, both side to side and up and down. Do the slanted layers change in direction, thickness, or color as you move across the rock face? If so, describe what you notice.
To complete this EarthCache, please include a photo of yourself, your group, or a personal item at the posted coordinates with your log.
- Make sure your answers to the questions above are not visible in the photo.
Arkansas Little Grand Canyon
Located just beyond the dam and spillway at Lower White Oak Lake, this beautiful site offers beautiful views and a chance to observe cross-bedding—angled sediment layers formed by ancient water currents.. The rock layers here are part of the Cane River Formation, a geologic unit dating back to the Tertiary Period (approximately 66–23 million years ago). This formation records the dynamic shifts of ancient environments, from swamps and floodplains to shallow marine waters.
After exploring the spillway, take a short walk to the nearby canyon floor (trust me, you want to do this), where you can see sedimentary rock layers up close. There’s also a nice 0.4-mile trail that loops around the Little Grand Canyon, giving you different views and plenty of photo opportunities. Note: A trail map provided by White Oak Lake State Park has been uploaded for reference.
Cross-Bedding
Cross-bedding is a geological feature found in sedimentary rocks, especially sandstones, where layers of sediment, called strata, are tilted or angled instead of lying flat. These slanted strata form when wind or water moves sediment across a surface, such as in deserts or riverbeds. As particles are pushed along, they build up and slide down the steeper side of dunes or ripples, creating angled layers called cross-beds. Over time, more sediment covers these strata, and they become buried and turned into rock through a process called lithification. Later, when erosion wears away the surface, these cross-bedding patterns become visible.
What makes cross-bedding interesting is that it holds clues about the environment where it formed. The direction of the angled layers shows the flow of wind or water at the time the sediment was deposited. For example, large sweeping cross-beds often form in deserts with high dunes and strong winds, while smaller, more tightly packed cross-beds usually come from river or coastal environments. By studying cross-bedding, geologists can learn not only the direction the water or wind was moving but also how strong or fast it was. For example, fast-moving rivers create steeper layers, while slower-moving water forms gentler slopes.
Cross-bedding also helps geologists piece together past landscapes and climates and is an important tool in stratigraphy, the study of rock layers or strata. In addition, cross-bedding is valuable in natural resource exploration, helping geologists find places where oil and gas might be stored by identifying ancient channels and porous rocks. These angled layers act as important records that help us understand how Earth’s environments and landscapes have changed over millions of years.
Acknowledgments
This EarthCache was written based on GSA and Geocaching guidelines. Permission for this EarthCache was granted by Poison Springs State Forest. A very special thank you to the Office of the State Geologist and AllThingsEarthCache for their guidance and expertise in order to successfully create this EarthCache.