  We present a sample of 74,216 M and L dwarfs constructed from two existing
catalogs of cool dwarfs spectroscopically identified in the Sloan Digital Sky
Survey (SDSS). We cross-matched the SDSS catalog with Gaia DR2 to obtain
parallaxes and proper motions and modified the quality cuts suggested by the
Gaia Collaboration to make them suitable for late-M and L dwarfs. We also
provide relations between Gaia colors and absolute magnitudes with spectral
type and conclude that (G-RP) has the tightest relation to spectral type for M
and L dwarfs. In addition, we study magnetic activity as a function of position
on the color-magnitude diagram, finding that Halpha magnetically active stars
have, on average, redder colors and/or brighter magnitudes than inactive stars.
This effect cannot be explained by youth alone and might indicate that active
stars are magnetically inflated, binaries and/or high metallicity. Moreover, we
find that vertical velocity and vertical action dispersion are correlated with
Halpha emission, confirming that these two parameters are age indicators. We
also find that stars below the main sequence have high tangential velocity
which is consistent with a low metallicity and old population of stars that
belong to the halo or thick disk.
