EMPLOYEE STATED HE WAS PUTTING UP CENTER LINES IN THE FACE OF #1 ENTRY AND WHEN WALKING HE STEPPED INTO AN UNEVEN DIP IN THE MINE FLOOR CAUSING LOWER BACK PAIN. HE VISITED A MEDICAL FACILITY ON 03-13-2000 WHERE HE WAS DIAGNOSED HAVING A L-S STRAIN. HE STARTED MISSING WORK ON 03-13-00 AND RETURNED ON 03-20-2000.