$10^{15}{\rm M_{\odot}}$ halo in the Hubble Volume simulation, where galaxies with SDSS colors and luminosities have been added to the simulation using the prescription outlined by Wechsler in this proceedings.[]{data-label="sim_cm"}](colmag.ps){width="7cm"}

To address the four challenges given above, it is vital that we construct realistic simulations of the C4 cluster catalog. This has now been achieved through collaboration with Risa Wechsler, Gus Evrard and Tim McKay at the University of Michigan. Briefly, mock SDSS galaxy catalogs have been created using the dark matter distribution from the Hubble Volume simulations (Evrard et al 2002)[^1]. The procedure for populating the dark matter distribution with galaxies is described by Wechsler in this proceedings, and in further detail by Wechsler et al (in preparation), but I present a brief overview here. The simulation we use provides the dark matter distribution of the full sky out to $z\sim 0.6$, where the dark matter clustering is computed on a light cone. Galaxies, with r-band luminosities following the luminosity function found by Blanton et al (2001) for the SDSS, are added to the simulation by choosing simulation particles (with mass $\simeq2.2\times10^{12}\,{\rm M_{\odot}}$ per particle) from a probability density function (PDF) of local mass density which depends on galaxy 