Something to do in California as well as the whole world is Geocaching. We did a post in April of 2013 that tells you more. Sometimes we go hunting usually on a Saturday on our way back from breakfast. We found 3 out of three.
From their website at: http://www.geocaching.com
Geocaching is a real-world, outdoor treasure hunting game using GPS-enabled devices.
Some are easy to find and some are hard. It is based on the size of the cache or the location. We found one the size of a small marble and one as big as a toaster. Clues are given by people who have found them but without giving it away too much. Sometimes there are no clues, you just go by your GPS.
In the photos below you can see examples. Inside they have a paper to sign your name. One was found under a big sign, what they call an easy grab(The happy Face) One was near a bridge nestled in between a guard rail. The last one that you can see hidden inside the bushes was the largest box we have found. There is a large community of people doing this, check it out!