Your emissions system isn't doing it's job. It may or may not have anything to do with mudding, or age of the vehicle, or something else. I get that code regularly and if I don't get it fixed by Nov I'll fail the emissions test.
First step I was told is to make sure fuel cap is on correctly, then clear the code. Did that, code came back in a few weeks. Next replaced the fuel cap, cleared the code, came back in a few weeks. Checked all the vacuum hoses and fittings, replaced one that seemed pretty old, cleared the code, came back in a few weeks.
Now a cleared code will come back in just a few days, so it's getting worse. I may next replace the evac vacuum pump that sits behind the driver side headlight.
But you might want to start with fuel cap and checking all your evap system hoses.