Gehrke, chief of the California Cooperative Snow Surveys Program, and White, a hydrographer with Southern California Edison, parked at Yosemite's Tioga Pass entrance, still closed for the winter season. Snow reached the roofline of the building next to the park's massive brown gate.
The pair set off on skis, guided by a sketch of the snow course crews have measured in Dana Meadows every winter since 1926. About 20 minutes later, they arrived at an old pine with an orange sign marking the beginning of the course.
Gehrke, who has been taking snow surveys for 30 years, 24 of them for the state, checked a compass and the map. White glided ahead to scout for the other end of the 1,400-foot-long plot. Once oriented, they took out a measuring tape and every 200 feet stopped to drill the sampling tubes into the snow.
They checked the toothed end of the cylinder for dirt to make sure they had hit the ground and not just a crust of ice, recorded the snow depth in a log hanging from Gehrke's neck and then weighed the snow core for water content. From that, hydrologists can calculate the volume of melt and runoff that nourish the state's reservoirs and aqueducts.