We're doing rolling rest days; I'm biking today and Abby and Beth tomorrow. I got up very early and was out the door before 6.
I outsmarted myself. I'd heard you had to ride on the I-90 shoulder to get into Rapid City, but Google Maps for bicycles suggested an alternate route using Airport Rd, Anderson Hill Rd, old US 14-16 and old US 14. This sounded good.
Old US 14 and 16 had been turned into a gravel road. You could see some rock-sized chunks occasionally, but definitely they had decided gravel was easier. After nearly 20 miles of this, I got on the I-90 shoulder.
We went auto touring in the afternoon to Mt. Rushmore, Wind Cave, and Custer State Park. After vain hunt for bison earlier in the day, we saw two rather distantly just before leaving Wind Cave and two near the highway in Custer -- the one on my side of the car was rather scraggly.