A large-eddy-simulation-based numerical investigation of a turbulent gaseous jet in crossflow (JICF) is presented. The present work focuses on cases with a steady crossflow and two different jet-to-crossflow velocity ratios, 2 and 4, at the same jet centerline velocity of 160 m/s. Emphasis is placed on the detailed flow evolution and scalar mixing in a compressible, turbulent environment. Various flow characteristics, including jet trajectories, jet-center streamlines, vortical structures, and intrinsic instabilities, as well as their relationships with the mixing process, are examined. Mixing efficiency is quantified by the decay rate of scalar concentration, the probability density function (PDF), and the spatial and temporal mixing deficiencies. Depending on the jet-to-crossflow velocity ratios, the wake vortices downstream of the injector orifice can either separate from or connect to the main jet plume, and this has a strong impact on mixing efficiency and vortex system development. Statistical analysis is applied to explore the underlying physics, with special attention at the jet-center and transverse planes.