Snakewater is a fictional city in Montana. In both the Jurassic Park novel and its film adaption Alan Grant and Ellie Sattler worked on a paleontological dig site located just outside the city in the badlands.
The city was invented by Michael Crichton in the first novel. In the movie the name wasn't replaced by a real city. The environment of the dig site implies the city must be near the Montanian badlands. In the novel John Hammond says that he will pick Alan and Ellie up with a plane at Choteau, and says you have to drive 2 hours by car to get there.
The site is well described in the novel. In the Cretaceous period it was an island in the Tethys Ocean near the shore of the main land. On the island Alan Grant found many eggs of Hadrosaurid dinosaurs. They were probably nesting on the island because then the juveniles were save for large carnivores. But there were also small carnivores like Velociraptor antirrhopus, which were also nesting there. All this is an obvious allusion to the "Egg Island" dig site in Montana, where Jack Horner discovered lots of Hadrosaurid and Troodon nests. Despite this, it is interesting to note that while Velociraptor antirrhopus and hadrosaurids could both be found in Montana, there were no hadrosaurids known from V. antirrhopus' time (115-108 MYA).