Passage 2.24.6
ὀλίγον δὲ ἀπωτέρω ἐν δεξιᾷ τῆς ὁδοῦ Χάον ἐστὶν ὄρος ὀνομαζόμενον, ὑπὸ δὲ αὐτῷ δένδρα πέφυκεν ἥμερα καὶ ἄνεισι τοῦ Ἐρασίνου φανερὸν ἐνταῦθα δὴ τὸ ὕδωρ· τέως δὲ ἐκ Στυμφάλου ῥεῖ τῆς Ἀρκάδων ὥσπερ ἐξ Εὐρίπου κατὰ Ἐλευσῖνα καὶ τὴν ταύτῃ θάλασσαν οἱ Ῥειτοί. πρὸς δὲ τοῦ Ἐρασίνου ταῖς κατὰ τὸ ὄρος ἐκβολαῖς Διονύσῳ καὶ Πανὶ θύουσι, τῷ Διονύσῳ δὲ καὶ ἑορτὴν ἄγουσι καλουμένην Τύρβην.
A short distance further, on the right-hand side of the road, there is a mountain named Chaon. At the foot of this mountain grow cultivated trees, and the water of the Erasinus river rises to view clearly there. Until that point, the river flows underground from Stymphalus in Arcadia, just as the streams called Rheitoi flow from the Euripus and emerge near Eleusis into the sea located there. Near where the Erasinus emerges from the mountain, the people sacrifice to Dionysus and Pan, and they conduct a festival for Dionysus as well, called Tyrbe.