Dark pigment extents from the petiole base well out into the blade. Lower pinnae are perpendicular to the rachis.
At first I had this as C. tenuis, which also occurs in the area, but upon looking at another key while trying to ID another fern, the perpendicular orientation of the lower pinnae struck me as inconsistent. Bulblet fern is previously recorded from this outropping.
Limestone (marble, actually) cliff species. See here for a shot of one of the bulbets on the underside, and the sori.
Bulblet bladder fern.
Cystopteris bulbifera (bulblet bladderfern) is a low-growing rock fern with creeping stems and narrow elongate deltate fronds which grow to 75 cm (30 in), native to eastern North America with two disjunct populations in the west. It is found only on calcareous substrates such as limestone. It commonly festoons limestone cave openings. While most commonly found on vertical rock faces, it also grows in rocky scree. C. bulbifera is unusual among ferns in producing bulblets along...