This paper studies the impact of social learning on the formation of close-knit communities. It provides empirical support to the hypothesis, put forth by the historian Fred Shannon in 1945, that local soil heterogeneity limited the ability of American farmers to learn from the experience of their neighbors, and that this contributed to their ``traditional individualism.'' Consistent with this hypothesis, I establish that historically, U.S. counties with a higher degree of soil heterogeneity displayed weaker communal ties. I provide causal evidence on the formation of this pattern in a Difference-in-Differences framework, documenting a reduction in the strength of farmers' communal ties following migration to a soil-heterogeneous county. Using the same design, I also show that soil heterogeneity did not affect the social ties of non-farmers. The impact of soil heterogeneity is long-lasting, still affecting culture and political preference today. These findings suggest that, while understudied, social learning is an important determinant of culture.