Lewis & Short

leucŏgaeus, a, um, adj., = λευκόγαιος, of white earth: colles, a chain of hills in Campania, where chalk was dug, Plin. 18, 11, 29, § 114; 35, 15, 56, § 174.
Here were the leucogaei fontes, Plin. 31, 2, 8, § 12.