We report trends in springtime ozone (O₃) and carbon monoxide (CO) at the Mt. Bachelor Observatory (MBO) in central Oregon, U.S.A. from 2004 to 2013. Over the 10-year period the median and 95th percentile springtime O₃ increased by 0.76 ± 0.61 ppbv yr⁻¹ (1.7 ± 1.4% yr⁻¹) and 0.87 ± 0.73 ppbv yr⁻¹ (1.5 ± 1.2% yr⁻¹), respectively. These trends are consistent with reported positive trends in springtime O₃ in the western U.S. In contrast, median CO decreased by −3.1 ± 2.4 ppbv yr⁻¹ (−1.9 ± 1.4% yr⁻¹), which is highly similar to springtime North Pacific surface flask measurements from 2004 to 2012. While a 10-year record is relatively short to evaluate long-term variability, we incorporate transport model analysis and contextualize our measurements with reported northern mid-latitude trends over similar time frames to investigate the causes of increasing O₃ and decreasing CO at MBO. We performed cluster analysis of 10-day HYSPLIT back-trajectories from MBO and examined O₃ and CO trends within each cluster. Significant positive O₃ trends were associated with high-altitude, rapid transport from East Asia. Significant negative CO trends were most associated with transport from the North Pacific and Siberia, as well as from East Asia. The rise in springtime O₃ is likely associated with increasing O₃ precursor emissions in Asia and long-range transport to the western U.S. The decline in springtime CO appears linked to decreasing Northern Hemisphere background CO, largely due to anthropogenic emissions reductions in Europe and North America, and also to a recently reported decline in total CO output from China caused by more efficient combustion. These springtime O₃ and CO trends suggest that hydroxyl radical (OH) mixing ratios in the North Pacific may have increased over the study period.