This is a network of new biking trails with a Jump Park, Downhill race track, cross country rides and downhill runs. All from beginner to Extremely nuts. This is Disney Land for the Mountain Biker. The resort is only two years old. The rental shop, bike shop, and restraunts are of the highest quality. $25 a day to ride as much as you want. If you want to go ride past the limits of your equipment you can rent theirs. If you get tired of riding you can do the zip line. It's a blast. The Chair is a High Speed Quad. You will get plenty of rides in. If you can't afford the rentals to stay over night, there is plenty of camping spots in the area for $9 a night. I recommend a weekend trip of this place and Brundage Mountain one hour away. Some say the trail riding there is even better than Tamarack.
http://www.tamarackidaho.com/summer_adventure/biking/index.php
I posted a picture of the map on how to get there from boise.
http://www.singletracks.com/item.php?c=1&i=2230