That map is not your only option. Seeing as you are in El Monte head over to the REI in Arcadia and see what maps they have for the Gabs. Again, the Robinson maps are quite nice as well. I have some for the Gabs. Keep in mind some sections of the range are still closed due to the Station Fire from a few years ago. Word around town is the ANF will reopen some areas around Memorial Day Weekend.

If you tell me a bit more what you are looking for I might be able to help. I have ridden and/or hiked most of the roads and trails in the ANF.

Other options include downloading an iPhone or Android app that will cache USGS topo maps on your phone. I have one for my Android phone called Backcounty Navigator Pro I plan to use in remote parts of Utah in a few weeks. The app did cost but wasn't much.

Another option is to the a program called ArcGIS Explorer Online from Esri, http://explorer.arcgis.com/ Once the app loads click the New Map button in the upper left of the page. From there click on the Basemap button (icon to the right of the Print button). Then select USA Topo Map. This will load seamless USGS Topographic maps for the whole of the US. (Disclaimer: I happen to work for Esri these days).

One last recommendation would be to post something on SoCal Trailriders Forum. There is a very active community of mountain bikes with lots of knowledge of our local mountains.