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We present redshifts and optical richness properties of 21 galaxy clustersuniformly selected by their Sunyaev-Zel'dovich signature. These clusters, plusan additional, unconfirmed candidate, were detected in a 178 square-degree areasurveyed by the South Pole Telescope in 2008. Using griz imaging from theBlanco Cosmology Survey and from pointed Magellan telescope observations, aswell as spectroscopy using Magellan facilities, we confirm the existence ofclustered red-sequence galaxies, report red-sequence photometric redshifts,present spectroscopic redshifts for a subsample, and derive R_200 radii andM_200 masses from optical richness. The clusters span redshifts from 0.15 togreater than 1, with a median redshift of 0.74; three clusters are estimated tobe at z > 1. Redshifts inferred from mean red-sequence colors exhibit 2% RMSscatter in sigma_z/(1+z) with respect to the spectroscopic subsample for z < 1.We show that M_200 cluster masses derived from optical richness correlate withmasses derived from South Pole Telescope data and agree with previously derivedscaling relations to within the uncertainties. Optical and infrared imaging isan efficient means of cluster identification and redshift estimation in largeSunyaev-Zel'dovich surveys, and exploiting the same data for richnessmeasurements, as we have done, will be useful for constraining cluster massesand radii for large samples in cosmological analysis.

Optical Redshift and Richness Estimates for Galaxy Clusters Selected with the Sunyaev-Zel'dovich Effect from 2008 South Pole Telescope Observations