Name That Trauma :: Reader Meander on Zombie Cowboy Goo

Hey Kindertrauma,

…This trauma has been severely bugging and alluding me for many years.

I remember seeing the movie when I was about 9 or 10. A modern day brother and sister ride around trying to find their parents and discover a strange town that is back in the Wild West Days. I remember the townsfolk ended up all being zombies that melted into green slime when killed. Also a major plot point revolved around the signature book in the old west hotel that the parents were staying at. Also I remember them trying to leave town in an old Cadillac but being blocked by a force field. I think when they found their parents they had no memory of the kids. I believe it takes place entirely at night.

Anyone know what this could possibly be? I've been trying to find this movie for years. The image of zombified cowboys melting into puddles of green goo terrified me and was ingrained in my brain forever.