A couple weeks ago, my family decided to take a day trip up to the Napa Valley to do some hiking and have a family adventure. We parked at the Bothe-Napa Valley park and hiked down the history trail past an old pioneer cemetery and ended up at the historic Bale Grist Mill. I have driven by this many times along highway 29, and have been intrigued, but never have stopped. 
This was our day. We paid our admission and waited for the next tour. Just the visitors center area was so cool! I love learning more about California history and pioneer days. The tour exceeded my expectations. The tour guide (and all the people working there) were all in historic costume. He spent about 20 minutes outside by the waterwheel explaining the history of the mill and the Bale family (the owners of the mill) and then he explained how the water wheel and mill worked. We then went inside and they started up the water wheel and showed us all the gears and machinery that went into it.
Some interesting facts I learned – the teeth of the gears are made of wood to prevent the build up of static electricity. Flour dust is extremely flammable and a spark from static could cause a massive explosion. The mill had equipment that not only mill the grain, but it also had grain elevators and equipment to separate the grain from the chaff and to separate the flour by type.
When we got home, my kids were so inspired by our visit, that they wanted to build a working water wheel. We looked into our craft stash and found everything we needed: 6 Dixie cups, small styrofoam plates, skewers, and straws.
The kids played with this for over an hour. My 7 year old got out the Lincoln logs and build a mill to go with the water wheel (all while dressed as a pioneer wearing the bonnet we got at the gift shop). My 6 year old son felt like we need to actually mill some grain so he got to work grinding bird seed into flour between two flat rocks. He is pretty much satisfied when he can bash anything with rocks.
I have made the activity into a STEM/History lesson in my TpT store. Check it out!
Sarah's STEM Stuff 