Those are the official mountain bike trails at Theodore Wirth park. Google Maps is bad for finding mountain bike trails--it doesn't show the other Twin Cities trails at Lebanon or Murphy-Hanrehan either. They're the sort of trails you could find if you wanted to, though, by some searching or asking at bike shops.

I agree in general, though. Even if you have your own routes or know friends who have theirs, this helps break out of that rut and find some new rides. This would have been great for finding rides just across the river in Wisconsin (though as-is it wouldn't help find hills. I've always wanted a map similar to this that showed all roads in terms of both ridability and steepness).