Why two identical pictures of El Capitan in Yosemite? They are not actually identical. They were taken simultaneously by a camera with two lenses set approximately two and a half inches apart - like your eyes - so the perspective is slightly different in each image. The result is a pair of pictures that when viewed through a stereoscope seem to pop out at you in 3-D. Stereoscopes were a popular means of viewing photographs that could not be printed in magazines and newspapers in the late 19th century.
For many early visitors the experience of seeing the Yosemite and Hetch Hetchy Valleys was like viewing a stereoscopic slide. As you will see in the activity below many of the features of the two valleys were remarkably similar.
Each item in the following list presents you with a pair of images for your comparison - one from Hetch Hetchy Valley, one from Yosemite Valley. Prepare a chart for each item like the one started for you below comparing two of Albert Bierstadt's paintings. Carefully record the similarities and differences that you observe.
image from Carleton E. Watkins, "El Capitan, 3600 ft. Yosemite," 1880. Downloaded April 2, 2017 from Wikimedia Commons.