Explanation of Region Maps

The San Gabriel Mountains are covered by seven region maps in order to show the hikes and trailheads more clearly. The regions have been defined as areas with trailheads accessed using the same basic initial driving directions. Thus all the trailheads in the San Gabriel River region are reached by using SR39 or roads very close to SR39; all the trailheads in the Islip region are reached by using the eastern part of SR2 or by roads close to it; etc.

Trailheads are the fundamental quantity shown on the map, since to hike any trail you must start at a trailhead. The maps are therefore optimized to show the trailheads clearly, along with all the access roads to them. The maps show all the major roads, but only show the minor roads which lead to trailheads. In some cases, the minor road continues on past the trailhead, but is not shown. The roads have been digitized by me from the USGS maps, and so don't follow every nuance of each road.

I have started plotting the hiking routes (trails or fire roads) on the maps in late 1999 as part of writing up my hikes, but this will take some time before a significant fraction are shown.

The axes of the maps are north latitude and west longitude in degrees. Note that USGS maps for the U.S. plot east longitude which is (360° - west longitude). I use west longitude so that my spreadsheet would plot the roads with west on the left.

In order to convey the information for a region more clearly, the maps are not true-scale maps. North-south distances are slightly different from east-west distances. You can figure out the scale by noting that one tic mark (0.1°) of latitude is 11 km = 6.9 miles, and one tick mark (0.2°) of longitude is 18 km = 11.5 miles. The tick marks will span different numbers of pixels for each regional map, since the scales had to be changed to best fit in all the information. As an example, one tick mark spans 56 pixels in latitude and 73 pixels in longitude for the nw region, making the scales 0.12 miles per pixel in latitude and 0.16 in longitude. The difference in scales is thus about 25% for that region.

The maps also show waterfalls and airplane crash sites that have remaining visible wreckage. I have tried not to block any of these locations with any of the labels. A plot without labels is always available for each of the regions from the link under the initial map.

The digital data for all plotted items is available separately by request, and someday I'll put those online.

Map legend

Blue crosses inside squaresTrailheads
Yellow boxes with numbers or abbreviationsThese identify trailheads within the region on that page. The text box gives either the hike number or location abbreviation explained in a table on that page.
Green boxes with numbers or abbreviationsThese identify trailheads from a neighboring hiking region (that region is not clickable on the map)
Blue-green filled trianglesWaterfall locations
Open green squaresSites of airplane crashes with remaining wreckage, accurate to 1' (~0.017° ~ 1 mile), courtesy of Chris Killian
Blue LinesPeripheral Roads and Freeways
Red lineAngeles Crest Highway
Greenish curvy linesMajor Forest Roads
Light gray linesMinor Forest Roads
Black solid linesCity streets
Black dashed linesHiking routes (trails or fire roads) which have an online guide.

See also a more complete explanation of the maps.

Go to Hikes in the San Gabriel Mountains

Copyright © 1997-1999 by Tom Chester.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Tom Chester
Updated 27 December 1999.