Unfortunately, after conducting extensive research, I was unable to find any information on a Whitewater River run called White Sand Mouth in Montana. Therefore, I cannot provide information on the ideal streamflow range (cfs), class rating, segment mileage, specific river rapids/obstacles, and specific regulations to the area.

I recommend contacting local rafting companies or the Montana Department of Fish, Wildlife, and Parks for more information on whitewater river runs in the state. It's important to always prioritize safety while engaging in any water-related activities and to follow all regulations and guidelines set forth by local authorities. Get driving directions.