(S (S (BASENP (NNS Authorities)) (VP (VBD evacuated) (NP (BASENP (DT an) (NN area)) (SBAR (WHNP (WDT that)) (S (VP (VBD was) (ADJP (NP (NP (BASENP (NN one-half)) (PP (IN of) (BASENP (DT a) (NN mile)))) (PRN (LRB -LRB-) (BASENP (QP (RB approximately) (NN 800)) (NN m)) (RRB -RRB-))) (JJ wide)))))))) (PERIOD .))