If i'm not mistaken, 7.7 miles. I am, however, not from the area.
The driving distance from Mount Rushmore National Memorial to the trailhead to Harney Peak which is located near Sylvan Lake Lodge in Custer State Park is 15 miles. Form the trailhead there is a 3.5 mile hike to the summit. Since Harney Peak is located in the Black Elk Wilderness, there are no roads leading to the top of Harney Peak. "As the crow flies", Harney Peak is about seven miles from Mount Rushmore.
That depends on how fast you hike
It would take a person about seven days to hike 63 miles if he/ she were traveling an average 9.5 miles per day.
In the Southeast corner of Arizona near the very tiny town of Bowie. Taking I-10, drive 20 miles or so past Willcox, AZ. Take State Road #186 to the Fort Bowie turn off. About eight miles down the dirt road, you will see the Fort Bowie Trailhead. A mile or so hike will take you to the ruins and a little visitor's center.
A great hike is from Edwards Crossing on the S. Fork of the Yuba River to Purdon Crossing. it's about 4 miles or so one way. The only problem is that you have to hike back to your car unless you have a car parked on the other end as well. It's a gorgeous hike.
They should expect to hike about 135/7, or about 19.3, miles each day.
11 hours
You have to either get there by boat or hike 13 miles.
It is less then four miles, do it should be a fairly easy hike.
Hike percentage = 100*(After Hike - Before Hike)/Before Hike
6.5 miles
In a straight line, you would be 8.06 miles (the square root of 65) away from home.