We did some epic rides in the area, this was more than 10 years ago, Tally Lake near Whitefish, some trails outside Columbia falls and esp out of Big Fork (Strawberry Lake area - Alpine Trail #7) ah hah! I just looked it up again - says "This ride is either the ultimate trail or the most brutal time you've ever spent riding and pushing your bikeā¦" I'm trying to remember which portion we did, but link below says it is considered one of the top 10 trail rides in the US and by others, one of the toughest 10 rides in the US! Lots of climbing, but once you are up, lots of open, scenic ridge riding, great views, great descents. Trails are in great shape since so dry there. Enjoy!
http://glaciercyclery.com/trails_rides.php
Also, Big Mountain (no Whitefish Mountain Resort) now has a bike park, I see!http://skiwhitefish.com/summer/mountain-biking/