We thank Clare Balboni, Oriana Bandiera, Robin Burgess, Maitreesh Ghatak and Anton Heil for feedback and the geographic data for the river erosion analysis; Nathan Barker, Gharad Bryan, Robin Burgess, Supreet Kaur, Daniel Keniston, Tavneet Suri, and Francesco Trebbi and seminar participants at UC Berkeley for insightful comments; Harneet Singh and Thu Tran for excellent research assistance; and Oriana Bandiera for extensive comments and discussions.