Mapping the expansion of the Universe gives clues to the underlying physics causing the recently discovered acceleration of the expansion, and enables discrimination among cosmological models. We examine the utility of measuring the rate of expansion, H(z), at various epochs, both alone and in combination with distance measurements. Because of parameter degeneracies, it proves most useful as a complement to precision distance-redshift data. Using the baryon oscillations in the matter power spectrum as a standard rod allows determination of H(z)/(Ωmh2)1/2 free of most major systematics, and thus provides a window on dark energy properties. We discuss the addition of this data from a next generation galaxy redshift survey such as KAOS to precision distance information from a next generation supernova survey such as SNAP. This can provide useful crosschecks as well as lead to improvement on estimation of a time variation in the dark energy equation of state by factors ranging from 15 50 %.