  The Gemini/HST Galaxy Cluster Project (GCP) covers 14 z=0.2-1.0 clusters with
X-ray luminosity of L_500 >= 10^44 ergs/s in the 0.1-2.4 keV band. In this
paper we provide homogeneously calibrated X-ray luminosities, masses and radii,
and we present the complete catalog of the ground-based photometry for the GCP
clusters. The clusters were observed with Gemini North or South in three or
four of the optical passbands g', r', i' and z'. The photometric catalog
includes consistently calibrated total magnitudes, colors, and geometrical
parameters. The photometry reaches ~25 mag in the passband closest to rest
frame B-band. We summarize comparisons of our photometry with data from the
Sloan Digital Sky Survey. We describe the sample selection for our
spectroscopic observations, and establish the calibrations to obtain rest frame
magnitudes and colors. Finally, we derive the color-magnitude relations for the
clusters and briefly discuss these in the context of evolution with redshift.
Consistent with our results based on spectroscopic data, the color-magnitude
relations support passive evolution of the red-sequence galaxies. The absence
of change in the slope with redshift, constrains the allowable age variation
along the red sequence to <0.05 dex between the brightest cluster galaxies and
those four magnitudes fainter. The paper serves as the main reference for the
GCP cluster and galaxy selection, X-ray data and ground-based photometry.
