Maps & Topography

A rendering in POV-Ray of the North Fork American near Dutch Flat

The graphical representation of the earth's surface is of intense interest to me. What is the shape of things, and how do these shapes arise? From childhood I have climbed any number of hills and mountains, seeking views of the terrain. From peaks along the crest of the Sierra Nevada, vast expanses of California and Nevada come into view. Over 150 years ago, Kit Carson remarked to Fremont, from a Sierran summit near Carson Pass, "There's that little mountain I told you about," pointing out Mount Diablo. This mysterious icon of the Central California landscape may be seen from almost anywhere on the Sierra crest, as well as from many locations in the lower elevations.

One of my favorite tools in studying landscapes is the computer. With the proper software, one can create a mesh of triangles which fits the topography of an area, and then look at the landscape from any angle, under any lighting conditions. The essential data I use is the U.S.G.S. Digital Elevation Model (DEM) 7.5 minute quadrangles. Data points are located at intervals of 30 meters on a grid of Universal Transverse Mercator coordinates. DEM data for California and other states may be found at

http://130.166.124.2/dems.html

Here is an example of a landscape rendering, using the freeware raytracer POV-Ray, of the terrain near where I live. It is a "top-down" view in which north is up, west is left, etc., and spans some fifteen by twenty miles. It comprises portions of Placer and Nevada counties; the North Fork American, Bear, and South Yuba river canyons are visible. Highway 80 traverses the area. A line connecting the northwest to the southeast corners of this map, roughly divides the region of stream-eroded terrain (to the southwest) from the region of glacially-eroded terrain (to the northeast). The peaks in the northeastern part of the map are around 8000 feet in elevation, while the North American, where it enters the map area on the southwest, is less than 1600 feet in elevation. Bowman Lake is near the top center, Lake Spaulding just north of I-80 near the center, of the map area. The landscape is composed of several million triangles. Portions of nine 7.5-minute DEM quadrangles were joined to make this rendering.

This rendering is of the same area as above, but provides an oblique view, from the southwest, looking northeast. On the right, the North Fork of the North Fork, with many of its tributaries, including Blue Canyon, can be seen; near the center, the twin canyons of Bear River and Steephollow Creek; on the left, the South Yuba, just above the town of Washington, and showing the confluence of Canyon Creek. Bear Valley and Lake Spaulding can be seen in the upper middle, Lake Valley Reservoir on the upper right. The towns of Alta and Dutch Flat are barely out of view at the bottom.

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