You have nothing to worry about. The penalty for having a pit bull in Denver is to show that you are permanently removing the dog from the city. Since you are just passing through even if for some odd reason your dog should escape your car and get picked up by animal control you can get them back by showing you are moving to LA.
As long as the dog is safely confined in your car (preferably by a crate for his own safety during the trip) you will have no problems. The crate prevents him from running off if there is an accident or jumping out when the door is opened.
The legal language is very scary but it all comes down to "If the dog is found to be a pit bull, it shall be destroyed, unless the owner produces evidence deemed sufficient by the manager that the pit bull is to be permanently taken out of Denver and the owner pays the cost of impoundment."
https://www.animallaw.info/local/co-...lls-prohibited
It also says you should transport them through in a crate. Which is a good idea whether or not there is BSL.