VSA is a nationwide vet service, not that cheap, sometimes in Petsmart stores. They do run emergency 24 hour hospitals in many areas, good in a pinch.
https://vcahospitals.com/find-a-hospita ... -directoryOther than that, you could use google, yelp, yp to prescreen vet offices on your route and near your intended camp sites. Hard to do in the heat of panic and no cell service.
We keep a well stocked first aid kit just for the dog, scanned copies of her vaccination records on our phones. Found out she was allergic to bee stings when we where probably 50 miles and 2 hours from a vet. Thankfully we had Benadryl in the kit as she was turning blue in under a minute. Robi is a retired AHT and glad she had those skills.