Thanks all for the positive thoughts! For those that wondered, yes, we looked into building permits and I've been on the phone and e-mail with the Shasta County building department for all the important questions before we put an offer. We are in escrow now and should be closing Monday.
The creek is seasonal and thus dries up late Spring so there are less restrictions than a year round creek. Last I was told (property is 6 hours away from where I live so haven't gotten to go back yet since we looked at it) there was water coming out the bottom of the dam. I do believe there is a good chance there is a Spring that is behind the dam but has been mostly covered over by the layers of silt over the years. Thinking about sinking a perforated pipe down into the ground behind the dam to see if anything comes out. We have water and power at the lot though I may consider adding a well later for pasture irrigation.
We won't be living in the 5th wheel or anything. It literally is just a parking space to keep it. I do have plans to build a metal RV shelter just to protect it from the elements. I will probably add solar on the roof of the shelter so we have power should we come and visit family in the area and want our own place to stay for a week or so at a time. For water (until pipes are run from the street) and sewer I am thinking about buying some large storage tanks that can sit under the trailer. Thinking a 500 gal or 1000 gal tanks should be plenty for a week at a time. I will pay a porta potty company to come pump out the black water tank as necessary.
Fingers crossed, I will see about hosting a Truck Camper meetup there next Spring like we did a couple of years ago on the coast. Maybe a two night thing and people can use it as a launchpad for bigger trips up the coast or something. Would be great to see you all again!