Absolutely there are mtb trails just east of the city in Hixson Forest. Check out humanpoweredtrails.com. I've not ridden there, but talkin to several people that built it and others that have raced down there it sounds like it is a very good system. One guy is the Pivot Cycles rep. Group rides every fri. night. Built alot more with imba in mind as compared to Decorah HPT. If LaCrosse don't satisfy you then head to Holzinger lodge in WInona Mn for some long ups and and smooth fast singletrack on top of the bluff then a real sack-it-up downhill. If you really need to ride up there go to Levi-Trow IMBA Epic is only about 1.5 hours from LC. Or Lowes Creek just south of Eau Claire is a super fun system also. On your way home hit Memorial Park in Red Wing, before you do some night climbing on the other bluff in town. Anyway the moral of the story is that there is plenty of riding around LaCrosse.
I've ridden all but Lacrosse so if you need beta let me know.
Dan