Introduced around 2000, the Garmin eTrex was the first GPS unit I used to trace a trail run. The GPS tracks were imported into TOPO! where the length of a run could be measured, an elevation profile generated, and the topography of the run examined.
Since the eTrex was designed to be used in an "orienteering" position -- flat in your hand in front of your body -- it would frequently have trouble receiving GPS satellite signals if hand-carried while running or hiking. About the time enterprising hikers and runners began to resolve this issue with creative hats, holsters and harnesses, Garmin released the Forerunner 201, greatly simplifying the task of tracing a route.
In 2005, while preparing a presentation about kayaking Piru Creek for a meeting with the Forest Service, I stumbled onto Keyhole.com. To say I was blown away by this bit of "Eureka" technology would be an a gross understatement. Now, in addition to seeing Piru Creek in photographs, and on a topo map, you could get a "before you paddle" preview using Keyhole -- even if you couldn't paddle class IV whitewater! Google acquired Keyhole in late 2004 and launched Google Earth on June 28, 2005.
Shortly after Google Earth was launched, SportTracks added the ability to launch Google Earth and view the GPS trace of a run or other activity. Since SportTracks could also directly import data from Garmin's Forerunner, the software made it very easy to view a run in Google Earth.
I've been working on updating the posts on Photography on the Run that reference a trail run to include a link to a Google Earth KMZ file. A KMZ file is just a zipped KML file, and either can be opened in Google Earth. A list of the trail runs with KMZ file links can be found by clicking "Google Earth KMZ Files of Trail Runs" in the sidebar.
These are actual tracks recorded by a GPS during a trail run and may contain GPS errors, route-finding errors, and wanderings that are difficult to explain. In a few instances tracks have been modified to correct errors, or to remove side excursions that are not part of the usual route, but not all errors have been corrected. No claim is being made regarding the appropriateness or suitability of the routes indicated. The GPS devices used to record these tracks include the Garmin Forerunner 201, Foretrex 201 and Forerunner 205; and the GlobalSat GH-615B.