A model ocean composed of four isopycnic layers on a β plane is spun up from rest by anticyclonic wind stress. Model equations are formulated in material isopycnic coordinates with no restrictions againist vanishing layer thickness. This permits separation of the western boundary current from the coastline and formation of coastal upwelling fronts. The optimum truncation properties of isopycnic coordinates with regard to frontogenesis are discussed and weighted against numerical stability problems associated with the outcropping of isopycnals at the sea surface. Examples of coastal upwelling fronts are presented.