We consider the problem of transmitting a number of distributed sources through an orthogonal multiple access channel to a common destination. We characterize the optimal tradeoff between the transmission cost and the distortion as measured against individual sources. The approach consists of two steps: (1) a multiple- letter characterization of the rate-distortion region for the multiterminal source coding; (2) a source-channel separation theorem ensuring that all achievable cost- distortion pairs can be obtained by combining the rate-distortion region and the orthogonal multiple access channel capacity region. As a corollary, we determine the optimal power-distortion tradeoff in a quadratic Gaussian sensor network under orthogonal multiple access, and show that separate source-channel coding strictly outperforms the uncoded (amplify-forward) transmission, and is in fact optimal in this case. This result is in sharp contrast to the case of non-orthogonal multiple access for which separate source-channel coding is not only suboptimal but also strictly inferior to uncoded transmission .