I think it is important for MTBers to be involved with the maintenance of the trails they use; in our local park, we probably put about 200 hours of work into the trails each year - sometimes more, sometimes less - but the trails are always clear & ready to ride. Most of the people who use the trails also work on them, or will contact some who does work on them if they find a problem. Except for racing, riders stay off the trails when it's muddy - let's face it - less repair required on both bike & trail!
If you are just getting into MTBing, you should take the time to find the local organizations which maintain the trails - not only to volunteer, but to educate yourself on proper trail building & maintenance techniques. Keeping trails open is usually a big part of any MTB group.
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As with mud, life, too, slides by.