HST F140W image, centered on CARLA J1017+6116. We show as circles the galaxies that are either spectroscopically confirmed at the cluster redshift (blue circles; Noirot et al. 2018) or selected as statistically belonging to the clusters (magenta circles; Mei et al. 2023). The black rectangle indicates the KCWI FoV. Red contours represent galaxy overdensity starting from S/N = 3, as indicated in Mei et al. (2023). The higher overdensity peak north of CARLA J1017+6116 is associated with a galaxy overdensity at z = 1.235 discovered by Noirot et al. (2018), while the central overdensity is associated with the CARLA cluster and our KCWI observations. The north overdensity could not be excluded in the image contours due to the specific color cuts implemented to identify overdensities.