Much of the comparative data used by the Southern Sierra CZO comes from collaboration with the Kings River Experimental Watersheds (KREW), a long-term integrated ecosystem research project conducted by scientists with the U.S. Forest Service, Pacific Southwest Research Station. KREW collects numerous water and soil samples from the Providence Creek headwaters. Water chemistry data is obtained from analyzing samples taken from various stream sites located within the P300, P301, P303 and P304 catchments. Soil chemistry data is obtained from samples taken from soil pits located in the P300 catchment. KREW uses a wide variety of methods for collecting water, soil and other samples from the Providence Creek headwaters, including stream discharge instruments, snow pillows, sediment basins, atmospheric deposition sensors and a grid of hundreds of resin lysimeters.