The posted coordinates are at an Anasazi eagle trap. This location highlights excellent examples of Bandelier Tuff.
Otowi Mesa is part of the Bandelier Formation. It is made up of Bandelier Tuff, which was deposited over a period of a few weeks in a violent eruption of the Jemez supervolcano.
In its major eruption 1.14 million years ago, the Valles Caldera volcano spewed out over 300 cubic kilometers of ash, mostly as the Bandelier tuff (tuff being a rock composed of volcanic ash). The Bandelier is an ash-flow tuff, meaning that it flowed from the volcano as a hot slurry of ash particles and gas (~500-700°C). This slurry, flowing faster that 100 km/hr, and travelled 25-35 kilometers from its source at the caldera. The Bandelier tuff is several hundred meters thick on average, thins to nothing far from the caldera, and is much thicker where it filled canyons. -- from BANDELIER TUFF - VALLES CALDERA
Bandelier Tuff is comprised of grains of rhyolite that erupted as pyroclastic flows, red-hot clouds of ash that flow along the ground. The ash was so hot that after it came to rest the grains within welded together into rock. Some of the welding was more effective, yielding harder rock, while in other parts the welding was less complete and yielded softer rock. The softer portions eroded very quickly when exposed to the elements, resulting in many holes and caves.
The Anasazi people took advantage of the softness of the tuff to expand small caves into larger ones that could be inhabited. They also worked the rock to form footholds to climb steep cliffs, deer and eagle traps (like the one here), and the famous "stone lions" in Bandelier National Monument.
To claim this cache find, please email or message me the answers to the following questions:
- Include the line "GC7QKM7 - Eagle Trap and Tuff" along with the names of the cachers in your group.
- Describe the texture, color, and hardness of the tuff at this site.
- Which tuff color is softest? Why do you think that is so?
- Which side of the mesa is steeper; north or south?
- How can you account for the difference?
- Do you see any bubble-like holes in the tuff near this site?
- If you would like to post a photo of yourself at the site as part of you log, by all means do so!