Question: when did the dust bowl end in oklahoma
[{'answer': '1940', 'provenance': [{'wikipedia_id': '59749', 'title': 'Dust Bowl', 'start_paragraph_id': 1, 'start_character': 341, 'end_paragraph_id': 1, 'end_character': 345, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '59749', 'title': 'Dust Bowl', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 1006, 'bleu_score': 0.5666769387542301, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9277500290167053424}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '59749', 'title': 'Dust Bowl', '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': 9277500290167053424}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '59749', 'title': 'Dust Bowl', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['The drought came in three waves, 1934, 1936, and 19391940,', 'The Dust Bowl was a period of severe dust storms that greatly damaged the ecology and agriculture of the American and Canadian prairies during the 1930s; severe drought and a failure to apply dryland farming methods to prevent the aeolian processes (wind erosion) caused the phenomenon. The drought came in three waves, 1934, 1936, and 19391940, but some regions of the high plains experienced drought conditions for as many as eight years.']}}]}, {'provenance': [{'wikipedia_id': '59749', 'title': 'Dust Bowl', 'section': 'Section::::Human displacement.:United States.\n', 'start_paragraph_id': 20, 'end_paragraph_id': 20, 'meta': {'evidence_span': ['Between 1930 and 1940, approximately 3.5\xa0million people moved', 'The Dust Bowl exodus was the largest migration in American history within a short period of time. Between 1930 and 1940', 'Some residents of the Plains, especially in Kansas and Oklahoma, fell ill and died of dust pneumonia or malnutrition. The Dust Bowl exodus was the largest migration in American history within a short period of time. Between 1930 and 1940, approximately 3.5\xa0million people moved out of the Plains states; of those, it is unknown how many moved to California. In just over a year, over 86,000 people migrated to California. This number is more than the number of migrants to that area during the 1849 Gold Rush. Migrants abandoned farms in Oklahoma, Arkansas, Missouri, Iowa, Nebraska, Kansas, Texas, Colorado, and New Mexico, but were often generally referred to as "Okies", "Arkies", or "Texies". Terms such as "Okies" and "Arkies" came to be known in the 1930s as the standard terms for those who had lost everything and were struggling the most during the Great Depression.']}}]}]