Oh, that's mapmyride! They always ignore any elevation gains less than 10 meters, and so their total elevations don't compare to other mapping sites or to GPS recordings.

Here's the same route from 2011 on ridewithgps. The route looks pretty much the same, but the 2011 version repeats a loop at the end, instead of at the beginning.

Ridewithgps reports 4700 feet of elevation gain.

I found the 2012 route: ridewithgps.com/routes/1650629

It's 5000 feet of climbing. The red elevation chart looks very hilly, but it compresses the whole 100 miles.

The few hills that hit 5% to 6% are pretty short, only about 100 feet of elevation. The big hill at the 72 mile mark is mostly under an easy 2% grade, and it's only 150 feet tall. One of the 6% hills is at the 60 mile mark, with 100 feet of elevation gain. You won't need any lower gears than you already have.

The 78 mile mark hill is 3.5 miles long and 200 feet high, but mostly 1% grade or less. That's easy, just shift down a few gears and spin up it. The 91 mile mark hill is similar, 1% for 2 miles. And the 29 mile hill is 2 miles, 150 feet of 1% grades, with a pair of level sections in the middle, and a 40 foot tall 3-4% top part--easy.

The section at the 11 mile mark and again at the 70 mile and 85 mile mark gets repeated, with different exits from the loop! I hope they have good signage or volunteers at those junctions!

Using ridewithgps:
Pull the Map list down at the top right and select Terrain to see the hills. Then zoom in all the way to see contour lines. Each contour line is 40 feet of elevation.

You can also select a hill by dragging a section of the red graph, then you can see the hill's grade and elevation gain from the Metrics tab at the right side of the page.