We report the discovery of a locus of binary stars in the Sloan DigitalSky Survey (SDSS) g-r versus u-g color-color diagram that connects thecolors of white dwarfs and M dwarfs. While its contrast with respect tothe main stellar locus is only ~1:2300, this previously unrecognizedfeature includes 863 stars from the SDSS Data Release 1 (DR1). Theposition and shape of the feature are in good agreement with predictionsof a simple binary star model that consists of a white dwarf and an Mdwarf, with the components' luminosity ratio controlling the positionalong this binary system locus. SDSS DR1 spectra for 47 of these objectsstrongly support this model. The absolute magnitude-color distributioninferred for the white dwarf component is in good agreement with themodels of Bergeron et al.