Sentence:Widely previously interpreted as precursory activity to the 1906 earthquake, they have been found to have a strong seasonal pattern and have been postulated to be due to large seasonal sediment loads in coastal bays that overlie faults as a result of the [e1]erosion[/e1] caused by [e2]hydraulic mining[/e2] in the later years of the California Gold Rush.
 e1: erosion. 
 e2 : hydraulic mining.
Answer: Cause-Effect(e2,e1)