This site will look much better in a browser that supports web standards, but it is accessible to any browser or Internet device.
You can scroll around here and find a trailhead near you. Some of these trailheads have links here to the site as well as other places. This map was generously created by Dave Walsh who has set it up as a collaborative effort of many mountainbikers. The contents of the map are growing everyday so you will need to zoom and scroll into your area of interest to see all of the content. While I can not attest to its complete accurancy, it is a great user-friendly resource.
For you geeks and curious map users out there, the interactive map above is not a direct link to the Google hosted map. The map above is from a datafed KML file hosted here that allows the users to avoid having to click between the mulitple pages of the Google Map. It typical can take up to three hours for new entries on the Google Map to fed into the map above. I'll also have to recreate the feed everytime the map grows to another page. When I last checked there were five pages of trailhead information on the Google Map.