Maybe I'm interpreting it the wrong way, but I don't see where there's a 23% grade that goes on for miles. Mile 7 to 18 looks to have an average grade of around 8-9% with a maximum of 24.2%.
I meant that the climb went on for miles and miles not that the 23% grade went for the whole distances. An average grade of 8 to 9% is steep enough. The 24% grade is just a little extra added to already painful ride.