1) Four essential tips.
a) Explain and show the local geology.
An EarthCache must show and describe the local geology at the location of the cache coordinates, it must describe what the visitor will see. This means that the cache description cannot only contain a general description of the feature. A mix of general and local description usually works best.
Describe what it is to see here, and why the visitor should go to this location.
b) Geology, geology and geology!
An EarthCache must give a lesson in geology and must therefore be about geology, nothing else. A shorter historical description, or similar, may be included but then at the end and not dominant.
EarthCaches must be about geology!
c) Are there any similar EarthCaches nearby?
An EarthCache must show a unique geological feature. This means there cannot be multiple EarthCaches on the same topic too close to each other, for example Giant kettles, Hot springs, Glacial erratic, (including other features depending on the region). This also applies on cache features on different rocks types on statues, sculptures or building stones in urban areas. These types of EarthCaches can't be too close to each other either. Please note, EarthCaches can be close to each other when they are on different topics.
Look nearby if there already is a similar EarthCache.
d) Keep the EarthCache to one topic.
An EarthCache usual works best when it covers one topic, not several. Some related topics can be described, but then there must be a strong connection. For example, land rising and shingle beach can work, but not land rising and grain size in minerals/rocks.
Try to keep the EarthCache to one topic, in description and logging task.
2) Four more things to consider.
a) The cache description should be written in your own words.
Do not copy whole texts or paragraphs from others material. Minor parts of the text can be quoted, remember then to put in a reference to the source.
b) Keep it simple!
Explain complicated words and concepts, the cache should be understood and loggable by visitors with basic/little knowledge in geology. More detailed expert-geology can be explained but should then be extra information and should not be necessary to complete the logging task.
c) Do not write too much.
A cache description that is too long will be read by few, and it becomes difficult to read. Keep the text short and simple. Remember that an image says more than a thousand words, so add pictures and/or illustrations to make a better lesson.
d) Organize the cache description.
A text with a good structure is much easier to read. Put in paragraphs and headings to make the text easy to follow and read. Place the logging task first or last, with its own heading so that’s easy to find.
3) The logging task.
The best kind of logging task is one that asks the visitor to go to the coordinates of the EarthCache and make a specific observation of a specific unique geological feature described in the cache. Then the visitor is asked to make some kind of interpretation, inference, prediction, etc, based on their own personal observations or measurements.
It is best to avoid simple measurements that do not involve further thought or interpretation, such as "measure the height" or "estimate the volume" or "count the number of". Alone, those questions do not help educate people about the earth. A better example would be something like "By reading the information on the cache, identify the different layers in the sedimentary rock and measure the thickest layer, try to explain why this layer is the thickest."
The focus of the questions has of course to follow the cache description and be about the local geology. The answers should make sure the visitors have been at the cache, and therefore should not be found on the Internet. It’s the answers to the question that shows that the person really did find the correct location.
The first question in the logging task should always be the strongest, the visitor should find the answer at the cache location and not on the Internet. The question should also make the visitor "think" a little, this means that the answers cannot be an easy measurement tasks or just "readable" from an information sign, you can use an information sign as information to the cache but just not to read the answer from.
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.