Las Campanas Observatory has been designated as the location for the Giant Magellan Telescope (GMT).
We report results obtained since the commencement, in 2005, of a systematic site testing campaign at LCO.
Meteorological (cloud cover, temperature, pressure, wind, and humidity) and DIMM seeing data have been
obtained at three potential sites, and are compared with identical data taken at the site of the twin Magellan
6.5m telescopes. In addition, measurements of the turbulence profile of the free-atmosphere above LCO have
been collected with a MASS/DIMM. We examine the contribution to the seeing arising from turbulence in the
ground layer (defined here as below an altitude of 500 m) through the difference between the turbulence integrals
in the full atmosphere (as measured by DIMM) and in the free atmosphere (as measured by MASS). Additionally,
we consider photometric quality, light pollution, and precipitable water vapor at LCO.