Here's the idea - on Saturday, May 1st, those participating in the event set out in the morning and hide a cache. It can be temporary or permanent (subject to approval by geocaching.com or another listing site), though permanent is preferable so we can increase the number available to newcomers.
At Noon we will all meet back up for a picnic potluck at the above coordinates and everyone gets index cards with the information on how to find all of the other caches. Burgers and hot dogs will be provided, so bring a side dish to share. (There will be a grill and a tabletop gas burner available if anyone doesn't eat beef or pork and wishes to cook something else.) After we've eaten, everyone heads back out to find the caches hidden that morning.
In the early evening (around 8 pm) we all get back together at Tower Pizza (N46* 50.590' W 114* 01.536') to share stories of the day and generally socialize.
Basic rules for hiding the days caches...
No scouting locations ahead of time. Checking maps, camouflaging containers, comparing rough coordinates to ensure sufficient distance from existing caches are all fine, but part of the fun will be heading to somewhere you aren't intimately familiar with and finding a good place to hide your cache.
Since folks are going to be attempting to find a number in the afternoon, keep the travel time from parking the vehicle to less than an hour round trip. If everyone hides caches with long walks not enough will get found by the end of the day, but hopefully we'll end up with a mixture of styles so that won't be an issue.
Using Clayjar's system, keep the ratings for both Terrain and Difficulty to 2.5 or less. Again, the idea is to give everyone the chance to hunt numerous caches during the day.
Any type of physical cache (traditional, multi, off-set, letterbox hybrid, or mystery) is acceptable as long as it conforms to the above limits. No involved physics problems, complicated cyphers, lengthy multicaches, difficult Internet searches or the like. For puzzle caches and such, keep the challenge to something that can be solved in the field.
Above all have fun and enjoy lots of caching for the day.