Hey JDG9_2000, I've had this same thing happen to me last week. I was at the Pedal Though the Pines ride in Bastrop, TX. I rode a lot of hills in and out of the saddle without much problem, but after about 17 miles of that I noticed a spasm in my right calf muscle. I had to keep the watts down to avoid the cramp, and could ride on to the the finish.
After the ride I was wondering, again, what was up. I seem to have this problem only with my touring bike. When I'm on my road bike I can go forever without any cramps or spasms. I don't think my cramps/spasms or yours are due to dehydration or potassium at this time of year. I think it has to do with your cleat position and/or the bike setup. I compared my Look cleat position from my road bike to the Shimano SPD cleat position on my touring bike. The SPDs were like 1-1.5cm forward on the shoe, so I moved them back.
Check your cleats and make sure the ball of your foot is directly over the pedal spindle. You may find that yours is too far forward. Also check your seat height. If it's too high or low that might create more motion and stress on your calf muscles.
~Rich in Austin