and takes you through the Mickelson Trail, which I have no idea what to expect (gravel/paved) from a quick Google Maps search.
Try looking at the official trail site:
https://gfp.sd.gov/state-parks/directory/mickelson-trail/I rode nearly all of it 2 years ago. It's beautiful, but not a "warm and fuzzy" trail like the GAP. Aside from a total of a total of a few miles in Deadwood and Custer, it's not paved. Surface varies between dirt, gravel and even sand. Trail conditions can change due to weather activity. I had to lift my bike over a downed tree near Mystic and skateboard through some washed out areas caused by heavy spring rains. It's also not flat. There are some significant grades for a rail-trail in places. While getting water is not a problem thanks to the cisterns nicely spaced along the trail, outside of Deadwood (the northern terminus), Hill City, Custer and Edgemont (the southern terminus), food sources are very limited. There is a bar/restaurant somewhere off the trail in Rochford and another once in Prichard. IIRC, neither is open on Sunday.
With all that said, It's a fabulous ride. I got on the trail at Engelwood after riding Spearfish Canyon and rode to Hill City, where I camped at Crooked Creek, which is just south of the center of town and which you can access right from the trail. The next day I finished up in Edgemont, where there is a municipal campground (with showers) at the south end of town.
Due terrain, trail surface, cattle gates you have to open and close and the numerous bridges (which you should slow down for due to possibly uneven transitions), budget more time than you may otherwise think you need.