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Remember:
The visit to the cache location combined with the cache description should make it possible to complete the logging task.
Visitors should reflect about what they see and read, and learn something about geology by completing the logging task.
A question like "describe what you see" is not good enough, visitors will see different things and there is no right answer. The question must be more specific.
4) Questionable/difficult topics, see link.
Waterfalls. A waterfall is by itself is not enough geology as a feature for an EarthCache, but with a description how the waterfall affects the local geology or how it has been created, the cache can work. Remember that the described geological feature must be visible at the site, and be able to build the logging task on.
Museums, or indoors in general. Earthcaches must involve, just like any other cache, GPS usage, so you cannot create an Earthcache that is completely indoors. However, if there is an outdoor stage/waypoint on the cache that involves GPS usage and it is possible to connect with something that you see indoors, the cache can work. The logging task must also include outdoor/GPS usage.
Statues, sculptures or other building stones. These kind of EarthCaches must describe the stone structure, minerals or fossils. Descriptions about rock types, formation or general description of the rocks origin is not good enough. The logging task must also be linked to the stone in place and its geological properties describe above.