Here is how you can do this for your own GPS logs. I will be writing this from the perspective of a Garmin Oregon 400t and a MacBook Pro. However, it is applicable to anyone.
Step 1. Clear your track before hitting the trail. Here's how on the Oregon 400t
Setup -> Tracks -> Reset -> Clear Current Track
Step 2. Set the record interval, the time between each point that your Garmin GPS records on the map. The more often it records a point, the faster your track log will fill up. If you want to record a very long track, set your record interval to "less often" or "least often" if you want a very detailed track, set your record interval to "more often" or "most often".
Step 3. Hike the trail.
Step 4. Save your track on the Garmin GPS unit. If you've followed the directions up till now, you should've started the trail with a clean slate on your track log. To save your track you just walked with a unique name to make it easier to find later, follow these directions:
Track Manager -> Current Track -> Save Track -> (name your track)
Step 5. Turn on your Garmin GPS unit then plug unit into the computer.
Step 6. Download Google Earth.
Step 7. Open your Garmin GPS unit's drive in Explore (Windows) or Finder (Mac) in my case, the drive mounts as "Garmin".
Step 8. Navigate to Drive "Garmin" -> Folder "Garmin" -> Folder "GPX"
|Custom name GPX File Located in the "GPX" Folder|
Step 9. Your track file will be located in the "GPX" folder where you're currently looking as (customname).gpx as long as you've followed all the directions. Copy this file to your desktop so it's easier to find. If you followed this procedure, go to Step 11.
Step 10. If you didn't clear your track log before hitting the trail it's still possible to recover just the trail segment.
Follow these instructions on your Garmin unit to save your trail hike as a unique track:
Track Manager -> Current Track -> Save Portion -> Determine which portion was your trail hike
by analyzing the date, time, and distance fields -> (name your track)
Now go back to Step 8.
Step 11. Open Google Earth, then select:
File -> Open -> Desktop -> Customname.gpx
It will ask you some preferences about how Google Earth should import your customname.gpx file, leave the options as they are and hit OK. Google Earth will import your GPX file and covert it to a Google Earth KML file for you.
Now you can view your GPX Garmin track as a Google Earth KML file overlaid on Google maps, it will even "play" it for you and show you exactly where you were hiking, and at what time. You can open the elevation plot by right clicking the track in the "My Places" bar on the left.