We present the final results from a targeted search for brown dwarfs with unusual near-infrared colors. From a positional cross-match of the Sloan Digital Sky Survey (SDSS), 2-Micron All-Sky Survey (2MASS), and Wide-Field Infrared Survey Explorer (WISE) catalogs, we have identified 144 candidate peculiar L and T dwarfs. Spectroscopy confirms that 20 of the objects are peculiar or are candidate binaries. Of the 420 objects in our full sample 9 are young (<~200Myr; 2.1%) and another 8 (1.9%) are unusually red, with no signatures of youth. With a spectroscopic J-K_s_ color of 2.58+/-0.11mag, one of the new objects, the L6 dwarf 2MASS J03530419+0418193, is among the reddest field dwarfs currently known and is one of the reddest objects with no signatures of youth known to date. We have also discovered another potentially very-low-gravity object, the L1 dwarf 2MASS J00133470+1109403, and independently identified the young L7 dwarf 2MASS J00440332+0228112, which was first reported by Schneider and collaborators. Our results confirm that signatures of low gravity are no longer discernible in low to moderate resolution spectra of objects older than ~200Myr. The 1.9% of unusually red L dwarfs that do not show other signatures of youth could be slightly older, up to ~400Myr. In this case a red J-K_s_ color may be more diagnostic of moderate youth than individual spectral features. However, its is also possible that these objects are relatively metal-rich, and thus have enhanced atmospheric dust content.

Cone search capability for table J/AJ/154/112/table3 (Results from spectroscopic classification and synthetic photometry)

Cone search capability for table J/AJ/154/112/table1 (Infrared Telescope Facility/SpeX (IRTF/SpeX) observations)

Cone search capability for table J/AJ/154/112/table2 (Gemini/Gemini Near-Infrared Spectrograph (Gemini/GNIRS) observations)

Cone search capability for table J/AJ/154/112/table4 (Unknown object properties)