The Mountain bike trails in the Kansas City metro and beyond are open much of the year, BUT damage to them when wet is a serious issue.
While the soil compositions vary to a degree, most are clay based and take some time to dry out. During the winter months that time can be more prolonged. An exception for some venues is when the ground is frozen solid.
Of all the local systems, the Lawrence River Trail, with it’s sandier track tends to open earlier.
The area trail stewards post the current status at Urban Trail Company. Note that the status only changes when an update is made.