Interesting, Mike. It was probably associated with the building of the Hetch Hetchy or Lake Eleanore dams. Here's the GMap4 link to the same view. Hetch Hetchy / Lake Eleanore Airstrip






And in searching on Google, I found this:

From Yosemite and the United States Navy
Quote:
For the next twenty-seven years, the Navy was absent from the park. However, in 1972, the Navy began to aid civilian search and rescue operations in cooperation with the National Search and Rescue Plan, and they have continued this practice to the present. The current presence of military aircraft within the boundaries of Yosemite National Park is not too surprising since they have been there since early in the twentieth century. The first military aircraft to visit the park was an Army Curtis JN4 which was piloted by Lieutenant J. S. Krull. Lieutenant Krull landed his craft in Leidig Meadow in the Yosemite Valley on 27 May 1919. Another aviation milestone was reached when Army Lieutenants Moore and Taylor completed their journey from San Francisco to Yosemite by landing their Curtis HN4s at Wawona on 8 December 1925. They touched down on a 3,000 foot airstrip which had been flagged out in Wawona Meadow. This experiment proved that the region could be serviced by air, and an airline out of Mariposa established regular service to Wawona.