Interesting route to take.
1st day shows as 53mi with 5253' of climb.
2nd day shows as 47mi with 2290' climb.
3rd day shows as 44mi with 2070' of climb in the first 15mi, then all downhill.
Why start and end in Rapid City when what you want to see if further west and all conveniently located right on the trail or on spurs?