Left: The distribution of stars and their 3D velocities within L20’s dust map viewed top-down (i.e. the view from the galactic plane). Gray shows the 3D dust corresponding to the OBP-B1- Cav dust cavity. Molecular cloud spines are shown in green, blue, and magenta for Orion A, B, and \(\lambda\), respectively. Stars are colored by their expansion velocity relative to the center of mass of the cluster. The orange point indicates the center, and orange line shows the direction to the sun.  Right: Radial profile of velocities for all the stars in OBP-B1. The blue line corresponds to the median velocity at that distance from the expansion center, and the shaded blue region corresponds to 1σ uncertainty. The dashed red line indicates where the turnoff occurs, which corresponds with the distance from the expansion center to the small foreground dust clouds.