Leaning against a wooden rail, environmental activist Geoffrey McQuilkin took stock of a parched geological wonderland that had been altered by a weekend deluge. The air was still thick with moisture, and this lake’s tributaries were cascading down from surrounding mountains, swollen by cargoes of fresh snowmelt and rain. Frothy whitecaps and wavelets lapped over grass meadows that had been dry ground only a week ago. The lake’s famous tufa formations — for so long a symbol of California’s lack of water — were capped with snow.