Determines masses for 7167 DA and 507 DB white dwarfs from SDSS Data Release 4 spectra by fitting synthetic model-atmosphere spectra, extending the log g grid to 10.0 to properly characterize the highest-mass (most compact) white dwarfs, several found up to ~1.33 solar masses. Establishes the empirical mass/density distribution of the white-dwarf population that Giddings-Mangano’s survival bound is checked against: an extremely dense, long-lived object type that would have trapped a cosmic-ray-produced stable BH, unlike ultra-relativistic BHs passing through Earth. relevance_note: A primary large-sample observational input for “white dwarfs exist, are extremely dense, and are populous” — the empirical substrate the white-dwarf-survival leg of Premise B needs to be about a real population, not a hypothetical one.