Get the indicated number of points in the indicated Quick Play challenge to unlock the corresponding challenge:

Bear Hunt: 60 or more points in Suppress The Outlaws
Fire Fight: 35 or more points in Bear Hunt
Hold The Fort: 125 or more points in Quail Hunt
Hollister's Dynamite Run: 7 or more points in Fire Fight
Suppress The Outlaws: 75 or more points in Hold The Fort