Due to its size and observable record of ancient rock, Mars is key to understanding crustal formation on planetary bodies, including Venus and Earth, which may have derived their first stable crust from mantle-overturn melting. Recent evidence that ancient martian crust contains an evolved component supports inferences of a pervasive, buried feldspathic component to the crust. With data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), we searched for feldspathic lithologies in pre-Noachian (older than ca. 4.1 Ga) crustal blocks uplifted by the Hellas basin-forming impact. We present evidence for ancient feldspathic rocks exposed across an ~2200 × 600 km area north of Hellas. Given their pre-Noachian age and stratigraphic position directly above putative mantle material, it is possible that these outcrops represent martian primary crust. Our discovery supports the hypothesis that there exists a pervasive, subsurface feldspathic component to the martian crust—a hypothesis that has, until now, been supported only by inferences from geodynamic data and small-scale observations.