Writing-on-Stone National Park is 45 km off of the highway which goes directly to the US border from Edmonton, Canada. When you arrive in Milk River (the last town before the border village), you go through the town and take the only road out (heading due east, there are signs!). The roads are completely straight and go on for hundreds of kilometers, so I can insure you that you will not be lost.
You can't adventure too far here, so only prepare for maybe a half day's trip. The park does close at night, but it is simple to get some incredible sunset or sunrise shots. On the route there, black dairy cows roam the fields completely un-monitored with no fences, so even for wildlife photographers this can be a fun trip. Also, there are rattlesnakes in the summer and fall seasons. Be aware =]
This place, though technically sitting in Canada, is just a few miles from a massive protected land which separates the United States and Canada. It is called Writing-on-Stone National Park, as scattered throughout the park there are cave drawings and writings from yesterday and centuries ago. When you adventure here, you may choose to go on a tour day, or completely independent. The tours have exclusive access to over twice the amount of protected land so I would highly recommend researching the time if you ever find yourself going North from Montana.