Lots of merchants, including gas stations, hotels and other - "we aren't sure exactly how much you will actually be charged until you leave" - establishments put holds on your credit card. I imagine a place like flying J who is patronized by trucks and large vehicles getting a lot of fuel, puts a larger holds to reduce the risk of pump and dash theft. The hold is usually removed within 24 hours and is pretty transparent to the customer. The card is not actually charged, it's just a hold in case they need to charge it if you didn't pay. it's fairly common.