In the early Universe, large gas reservoirs dominated the baryonic mass of galaxies, and fueled a rapid increase in cosmic star formation, peaking at a rate 10 times higher than what is observed locally. Most of our knowledge of these early galaxies has come from studying stellar light and emission lines from the hot, ionized gas of the interstellar medium, but it is the cold molecular gas -- typically traced by CO emission -- that provides the natal material from which stars form. With sensitive instruments like the VLA and ALMA, CO emission has been observed out to z~6, but only in the most massive and luminous of systems. Less luminous systems are observationally difficult to individually detect, but may be detected in aggregate with the technique of "intensity mapping". In this talk, I will present the first results from COPSS -- an intensity mapping experiment designed to measure the abundance and evolution of molecular gas at z~3. I will present the results of our first analysis, making use of 1400 hours of archival observations with the SZA to place the first-ever constraints on the CO power spectrum at z~3. I will also describe the present state of our second analysis, which makes use of 5000 hours of new observations with CARMA.