got the length of two of them from an article about parts of the trail opening
http://www.americantrails.org/resour...kotaOpens.html
I have ridden the entire length of the trail 3 times via the mid sept sd parks dept mickelson trail trek my memory is none of the tunnels are very long
while planning your trip note each section custer to edgemont, custer to rocheport and rocheport to deadwood has a different personality
if i had to pick just segment to do a round trip it would be mystic to rocheport it tends to follow a creek bed and will likely have some great
colors in the fall lunch in rocheport and downhill back to mystic second hill city to custer lunch in custer
crazy horse and lots of rock outcropping