Gmap4 US Topographical Maps
Gmap4 is a Google Maps based viewer for detailed topographic maps of the USA and Canada. Gmap4 can read and display GPX and KML files and comes with a detailed help file and a ‘Quick Start’ guide.
This map shows most of the USA and Canada. To view the topographical map open the menu in the upper right and select MyTopo.
It is also possible to view KML files with Gmap4, by adding some parameters to the map URL. This link loads a trail from a specified KML,
If you examine the URL closely you can see the parameters that you can change:
q = URL to a KML file
t = Map type
ll = Center of the map
z = Zoom level
In addition to KML files and GPX files, Gmap4 can now also read Google MyMap files.
The Gmap4 Help file contains step-by-step instructions for placing a KML file online by saving it as a Google MyMap. This is an easy and free way to place a KML file online so it can be viewed by Gmap4.
The topographic map tiles displayed by Gmap4 come from MyTopo via their API. If you want to use the MyTopo tiles yourself with the Google Maps API, then this post by Chris Schneider (to the Google Maps API Google Group) should be of help.