  The Cl 1604 supercluster at z~0.9 is known to contain at least four distinct
member clusters, separated in both projection and redshift. In this paper we
present deep, multicolor wide-field imaging of a region spanning ~45' on a
side, corresponding to 21 h^{-1}_{70} Mpc (physical) at the supercluster
redshift. We select galaxies whose colors correspond to those of
spectroscopically confirmed cluster members in the r' vs. (r'-i')
color-magnitude diagram. Using an adaptive kernel, we generate a map of the
projected red galaxy density and identify numerous new candidate clusters which
are likely supercluster members. Assuming that all of the density peaks are
associated with the supercluster, its transverse size is ~10 h^{-1}_{70} Mpc,
which is still significantly smaller than the nearly 93 h^{-1}_{70} Mpc depth
in redshift space.
