Large-scale observing systems are poised to become the dominant means of study for a variety of natural phenomena. These systems are comprised of hundreds to thousands of instruments that must be queried, managed, and shared in a scalable fashion. Services-oriented architectures (SOAs) are widely recognized as the preferred framework for building scalable and extensible cyberinfrastructure. By applying SOA concepts, we created a framework for organizing observing system resources. Guided by this framework, we developed web services, custom workflow applications, and an integrated user interface of monitors and controls for managing instruments in large-scale sensor network observing systems. In this paper we present our approach and discuss its application to the NSF EarthScope USArray large-scale seismic observing system.