Question: through what process has the colorado river created the grand canyon in the usa
[{'answer': 'erosion'}, {}, {'provenance': [{'wikipedia_id': '46989', 'title': 'Grand Canyon', 'start_paragraph_id': 16, 'start_character': 0, 'end_paragraph_id': 16, 'end_character': 383, 'bleu_score': 0.970362113628587, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14123264136851803285}, 'section': 'Section::::Geology.\n'}]}, {'provenance': [{'wikipedia_id': '46989', 'title': 'Grand Canyon', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 0, 'bleu_score': 1.0, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14123264136851803285}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '17469702', 'title': 'Provo Canyon', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['The Provo River has carved out the canyon over time along with the forces of erosion', "Provo Canyon is a canyon in unincorporated Utah County, Utah, USA and Wasatch County, Utah. Provo Canyon splits between Mount Timpanogos on the north and Mount Cascade on the south. The canyon extends from Orem on the west end to Heber City on the east. The canyon's main thoroughfare is U.S. Route 189. Attractions in Provo Canyon include Vivian Park and Bridal Veil Falls. The Heber Valley Historic Railroad operates passenger trains through the canyon. The Provo River has carved out the canyon over time along with the forces of erosion."]}}]}, {'provenance': [{'wikipedia_id': '46989', 'title': 'Grand Canyon', 'section': 'Section::::Geology.\n', 'start_paragraph_id': 17, 'end_paragraph_id': 17, 'meta': {'evidence_span': ["the rate of erosion and cut nearly all of the Grand Canyon's current depth by 1.2 million years ago. The terraced walls of the canyon were created by differential erosion. Between 100,000 and 3 million years ago,", "the rate of erosion and cut nearly all of the Grand Canyon's current depth by 1.2 million years ago. The terraced walls of the canyon were created by differential erosion. Between 100,000 and 3 million years ago, volcanic activity deposited ash and lava over the area which at times completely obstructed the river. These volcanic rocks are the youngest in the canyon. The Ancestral Puebloans were a Native American culture centered on the present-day Four Corners area of the United States. They were the first people known to live in the"]}}]}]