The overlap between NY 19A and NY 436 comes to an end northwest of Portageville at a junction known as Bigelow Corners. NY 436 heads west into the town of Pike; however, NY 19A continues northward along the Southern Tier Line, a railroad line owned by the Norfolk Southern Railway, into the town of Castile. Here, the forests that had surrounded NY 19A begin to give way to open fields as the route heads away from Letchworth State Park. NY 19A meets NY 39 just southwest of the village of Castile, and the two routes overlap for a mere into the village limits. After crossing the village line, NY 19A leaves NY 39 and heads northwest into the town of Gainesville. The route turns back to the north just west of the town line and continues onward through fields and forests toward the village of Silver Springs.