The photo above shows a layer of mid-level clouds and their shadows as observed from an altitude of approximately 8,500 ft (2,590 m). Photographer: William Briscoe; William’s Website
It was taken flying east to west somewhere over the desert of southeastern California — the camera is facing northwest. Note the thin beams of light filtering through the altocumulus cloud deck. From this perspective, the picture seems as if it could have been snapped by a scuba diver. Shadows from the clouds projected upon the desert floor look much like undulations in sand in shallow water. In actuality, the dappled surface results from the interplay of nearly vertical sunbeams and cloud shadows — crepuscular rays. The wavy appearance of the shadows is caused by uneven topography.