Alsace is rich agriculturally (especially in the plain between the Rhine River and the Vosges Mts.), geologically (potassium exploitation in the Mulhouse area ranks France among the top worldwide producers), and industrially. Strasbourg is the ancient capital and the leading industrial center. Textile industries are located in the Mulhouse-Colmar area, and wines (notably Riesling) are produced there. Hydroelectric plants are at Kembs and Ottmarscheim. Virtually the whole population speaks French, but a very large majority have also retained their German dialect. About 75% of the population is Roman Catholic. Alsace retains many old customs such as the wine and harvest festivals.