Question: when did the tech boom start in san francisco
[{'answer': 'Silicon Valley', 'provenance': [{'wikipedia_id': '26976', 'title': 'Silicon Valley', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 14, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '26976', 'title': 'Silicon Valley', 'start_paragraph_id': 1, 'start_character': 55, 'end_paragraph_id': 1, 'end_character': 718, 'bleu_score': 0.6057331330366871, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17789045006085921239}, 'section': 'Section::::Abstract.'}]}]