( ( Because ( ( the ( best ( beaver pelts ) ) ) ( were ( found ( in ( the ( Rocky Mountains ) ) ) ) ) ) ) ( , ( ( they ( ( trapped there ) ( in ( the icy ) ) ) ) ( ( ( ( streams ( during ( the winter ) ) ) , ) ( often alone ) ) . ) ) ) )
(ROOT (S (SBAR (IN Because) (S (NP (DT the) (JJS best) (NN beaver) (NNS pelts)) (VP (VBD were) (VP (VBN found) (PP (IN in) (NP (DT the) (NNP Rocky) (NNPS Mountains))))))) (, ,) (NP (NP (PRP they)) (VP (VBN trapped) (ADVP (RB there)) (PP (IN in) (NP (DT the) (NN icy))))) (VP (VBZ streams) (PP (IN during) (NP (DT the) (NN winter))) (, ,) (ADVP (RB often) (RB alone))) (. .)))
Because the best beaver pelts were found in the Rocky Mountains, they trapped there in the icy streams during the winter, often alone.
(ROOT (S (NP (NNS Streams)) (ADVP (RB often)) (VP (VBP start) (PP (IN in) (NP (NNS mountains)))) (. .)))