Well, it seems overly simple to call it just geography.
Under the "geography" umbrella we're learning about the natural rock, land, and water formations.
You can file learning about each state's Native people, as well as the current state productions and interesting things that each state is well known for, under "social studies."
Writing it all out and calculating things like mileage and estimated gas usage from place to place counts, of course, as "handwriting" and "math."
In the "science" category we're learning about native plants and wildlife, as well as fossils that can be found to give us a clue about how that area has been throughout history.
And speaking of "history", we're getting a good dose of it, as we learn about how each state was settled, how it has grown and changed, and Presidents and other important people who have come from each state.
This summer we're going on a 3500 mile road trip to attend my sister's wedding in Maine and visit family and friends on the east coast. We've done the trip from Maine to here in California before, when we moved here in 2011, but this is our first time doing the reverse journey and also our first time as a homeschooling family. It seems very natural to turn this into a homeschooling project!
What we're currently doing is, one state at a time, reading books about each state (nothing fancy, just books I picked up from the kids section at the library) and writing information on some simple response sheets that I created. One of the sheets asks for the official "state information" for each place along our route, which is usually contained in a simple list format towards the end of the book. These are the simple facts such as state nickname, state motto, state bird, state fossil, etc. The other sheet has questions that he can pull the answers to from the reading, so he's learning some great research skills at the same time. Some examples are "What types of wild animals can be found in this state?" "What kind of food is produced here?" and "What Native American people came from this state?"
Along the way we are supplementing this with documentaries and video clips and other sources of information about the states we'll be traveling through, and in particular the places where we'll be stopping to explore for a while.
Of course the culmination of all of this learning will be the road trip, which is going to take approximately 12 days. We'll have the binder that we've been filling with all of this information, as well as art that the kids have created about the trip and about each place we learn about, and along the way he will be able to share interesting information with the rest of us as we travel towards each new place. There will be places that the kids identify along the route for us to stop and take a break - for instance, as he was reading the book about Kansas, we learned that there is an insect zoo there, and it's right along the route where we'll be driving! The boys were both very enthusiastic about that, so I'll research it a little further and if it's going to be open and we can afford it, we'll stop for an afternoon there. Each state will have a couple of fun tidbits like this for us to check out.
For the route out there we need to be fairly direct, since we have a deadline (getting there in time to help set up for the wedding) but on the way back we may meander a little bit. My oldest even asked if we could travel along a bit more of a northern route so that we could add some states to the return trip that are new to everyone in the family. I loved that request! When he asked me that, it felt like we were really "getting" it, that he was really interested and engaged.
As this trip gets closer it becomes quite nerve wracking to think of everything that needs to be ready in time to go, but I breathe through it and just think of what an incredible learning experience this is, for EVERYONE in the family! We are all learning together about so many different things, and these are important life skills. Academia aside, our kids are learning how to plan and execute a big road trip. That's so huge! I sincerely hope that when they are grown up that they do some traveling and adventuring on their own, and being part of experiences like this as a family is teaching them how to do that. I believe that this is a life skill to teach our kids as much as we teach them cook and clean and read and write.