THE WEATHER WAS CLEAR. THE OPERATOR SAID THAT HE WAS RUNNING THE FILL AND AS HE MADE A PASS THAT A R-50 DUMPED BESIDE HIM AND WHEN BACK UP HE BACKED OVER A ROCK THAT HAD COME OUT OF THE R-50. HE SAID THAT WHEN THE DOZER BACKED OVER IT AND LANDED THATS WHEN HE HURT HIS BACK.