Here is about every place I know to look to find out when & where the races are happening. Here is everything from leg shaven roadies to trail riding hippys, its all here.
Prologue Cycling Magazine - Great site for Midwest cycling/racing news. Pretty inclusive calender. I have only noticed a handful of MTB races not on it.
United Federation of Dirt - MTB Paradise! Race calender and results only.
Psycowpath - Nebraska MTB Series.
Local Cycling dot com - Another pretty good site to get some info. I see mostly Road and Cross than MTB, but its there too.
Earthriders Forum - MTB race forum here. If your wondering why something is the way it is in the MTB race scene, you will find it here. Great site if there is a looming thunderstorm, etc, before a MTB race to see if its happening or not.
There you have it! Hope it helps you schedule your upcoming season..
|Pic from the ever popular BoneBender MTB Race 2012|