For years, scientists said that it had been carved slowly by the Colorado River, over a period of milllions of years.
(scientists; said; that it had been carved slowly by the Colorado River, over a period of milllions of years; T:For years) Context(scientists said,List([11, 26))):(it; had been carved slowly; by the Colorado River; T:over a period of milllions of years)
scientists said,List([11, 26))
scientists it
said had been carved slowly
that it had been carved slowly by the Colorado River, over a period of milllions of years T:For years
by the Colorado River T:over a period of milllions of years