(S (S (BASENP (DT The) (NN avalanche)) (VP (VP (VBD started) (PP (IN at) (NP (BASENP (DT an) (NN elevation)) (PP (IN of) (BASENP (NN 3,600) (NNS meters)))))) (CC and) (VP (VP (VP (VBD went) (PP (IN down) (BASENP (DT the) (NN mountainside)))) (PP (IN for) (BASENP (QP (RB nearly) (NN 100)) (NNS meters)))) (COMMA ,) (S (VP (VBG leaving) (S (BASENP (DT a) (NN trail)) (ADJP (BASENP (NN 50) (NNS meters)) (JJ wide)))))))) (PERIOD .))