Diffuse emission of magmatic CO₂ is one of the main indicators of volcanic unrest at Mammoth Mountain, but the presence of deep seasonal snowpack at the site has hindered year-round CO₂ flux observations. A permanent eddy covariance station was established at the largest area of diffuse CO₂ degassing on Mammoth Mountain (Horseshoe Lake tree kill) that measured CO₂ fluxes (F_c) and meteorological parameters on a half-hourly basis. From July 22, 2014 to May 24, 2020, F_c ranged from −35 to 10,546 g m⁻² d⁻¹. F_c decreased on average by 53% over the study period, tracking the long-term decline in CO₂ emissions following the last major increase that occurred at the Horseshoe Lake tree kill area from 2009 to 2011. Statistical and spectral analyses were applied to the F_c and ancillary meteorological parameter time series to understand (1) relationships between these parameters, (2) their dominant periodicities, and (3) changes in F_c that may be unexplained by meteorological forcing. Variations in detrended F_c (F_cdt) were most strongly correlated with wind direction and atmospheric temperature, followed by atmospheric pressure on diurnal to annual time scales, but wind direction likely exerted the most direct control on F_cdt. Comparison of the smoothed (180-d span) F_cdt time series to the time series of average-daily snow water equivalent measured ~1 km away suggested that snowpack may have suppressed CO₂ emissions. No evidence of a change in CO₂ emissions related to the last major seismic swarm beneath Mammoth Mountain on February 2–18, 2014 was observed.