First the Merced River dug a deep canyon to start the valley.
(the Merced River; dug; a deep canyon; to start the valley; T:First) Context(the Merced River dug,List([6, 26))):(the Merced River; dug a deep canyon to start; the valley)
the Merced River dug,List([6, 26))
the Merced River the Merced River
dug dug a deep canyon to start
a deep canyon to start the valley T:First
the valley