[written March 28, 2007]
I have posted, on YouTube, a 30-second animation depicting the terrain around the North Fork of the American River. The "virtual landscape" is seen as if from perhaps thirty miles above, looking straight down, and oriented like most maps, with north up, east right, west left, south down. See
The area encompassed by the animation extends from Colfax on the west (lower left) nearly to Donner Pass on the east (upper right); one can see, from north to south (top to bottom), portions of the canyons of the South Yuba, Steephollow, Bear River, Blue Canyon, North Fork of the North Fork American, North Fork American, Indian Canyon, Shirttail Canyon, North Fork of the Middle Fork American, Middle Fork American (with French Meadows Reservoir seen on center right), and at the lower right, a bit of the Rubicon and Hell Hole Reservoir.
The animation involves use of a sun position algorithm to move a virtual sun across the sky, along the exact path it would follow on the Vernal (and therefore, also, Autumnal) Equinox.
On the equinoxes, the sun rises due east and sets due west. As it passes through the southern sky, midway between dawn and sunset, it rises high enough to fairly well fill the various canyons with light; but in the early morning and late afternoon, deep shadows haunt the canyons, and the relief of the landscape is seen to its best advantage. Relief-enhancing low-angle illumination is usually preferred by those geologists who use aerial photos to trace the courses of fault zones, or to study geomorphology. I use this same trick on my "virtual" landscapes.
Here, about five minutes separates one frame of the animation from the next. I begin before dawn and finish after sunset. In the YouTube movie, the animation runs twice, and the second time through, little flashing lights were attached to Lovers Leap, on the west at Giant Gap, and Snow Mountain, on the east at the Royal Gorge. The two points are about twenty air miles apart.