Procedure to convert Garmin tracks to Google KMZ (compressed KML) tracks.

Manually edit original segments into one file. Use a pure text editor, not a word processor. In this example the segments are separated via the header for each segment. Note that the color of each segment can be edited. In this case alternated between red and blue. Make sure the html tags are matched within each segment and the overall file.

<?xml version="1.0"?>
<gpx xmlns="http://www.topografix.com/GPX/1/1"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns:wptx1="http://www.garmin.com/xmlschemas/WaypointExtension/v1"
 xmlns:gpxtrx="http://www.garmin.com/xmlschemas/GpxExtensions/v3"
 xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1"
 xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3"
 xmlns:abp="http://www.garmin.com/xmlschemas/ActivityExtension/v1"
 xmlns:adv="http://www.garmin.com/xmlschemas/AdventuresExtensions/v1"
 creator="Garmin Desktop App" version="1.1"
 xsi:schemaLocation="http://www.topografix.com/GPX/1/1
 http://www.topografix.com/GPX/1/1/gpx.xsd
 http://www.garmin.com/xmlschemas/WaypointExtension/v1
 http://www8.garmin.com/xmlschemas/WaypointExtensionv1.xsd
 http://www.garmin.com/xmlschemas/TrackPointExtension/v1
 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd
 http://www.garmin.com/xmlschemas/GpxExtensions/v3
 http://www8.garmin.com/xmlschemas/GpxExtensionsv3.xsd
 http://www.garmin.com/xmlschemas/ActivityExtension/v1
 http://www8.garmin.com/xmlschemas/ActivityExtensionv1.xsd
 http://www.garmin.com/xmlschemas/AdventuresExtensions/v1
 http://www8.garmin.com/xmlschemas/AdventuresExtensionv1.xsd">
    <metadata>
        <link href="http://www.garmin.com">
            <text>Garmin International</text>
        </link>
        <time>2011-11-25T21:08:16Z</time>
        <bounds maxlat="42.008995385840535" maxlon="-71.768572283908725" minlat="41.976003041490912" minlon="-71.785566257312894"></bounds>
    </metadata>
    <trk>
        <name> Segment 1</name>
        <extensions>
            <gpxx:TrackExtension>
                <gpxx:DisplayColor>blue</gpxx:DisplayColor>
            </gpxx:TrackExtension>
        </extensions>
        <trkseg>
            <trkpt lat="42.008775193244219" lon="-71.785535579547286">
                <ele>203.4561767578125</ele>
                <time>2011-11-25T17:49:13Z</time>
            </trkpt>
            <trkpt lat="42.008759686723351" lon="-71.785566257312894">
                <ele>216.4339599609375</ele>
                <time>2011-11-25T17:50:01Z</time>
            </trkpt>
...etc....

...etc....

...etc....

...etc....

      <trkpt lon="-71.68995195999742" lat="41.43860762938857">
        <ele>18.200000762939453</ele>
        <time>2012-02-11T18:17:12.000Z</time>
      </trkpt>
      <trkpt lon="-71.68997568078339" lat="41.43854786641896">
        <ele>18.399999618530273</ele>
        <time>2012-02-11T18:17:18.000Z</time>
      </trkpt>
    </trkseg>
  </trk>
<trk>
        <name> Segment 8</name>
        <extensions>
            <gpxx:TrackExtension>
                <gpxx:DisplayColor>red</gpxx:DisplayColor>
            </gpxx:TrackExtension>
        </extensions>
        <trkseg>
            <trkpt lat="41.438066326081753" lon="-71.690199309960008">
                <ele>26.5736083984375</ele>
                <time>2012-05-06T14:41:50Z</time>
            </trkpt>
            <trkpt lat="41.438043359667063" lon="-71.690243482589722">
                <ele>23.208984375</ele>
                <time>2012-05-06T14:42:17Z</time>
            </trkpt>
...etc....

...etc....

...etc....

...etc....

	    <trkpt lat="41.341393394395709" lon="-71.694118939340115">
                <ele>1.0986328125</ele>
                <time>2012-05-06T19:24:41Z</time>
            </trkpt>
            <trkpt lat="41.341402446851134" lon="-71.694116676226258">
                <ele>1.579345703125</ele>
                <time>2012-05-06T19:24:52Z</time>
            </trkpt>
        </trkseg>
    </trk>
</gpx>

• Open Google Earth.
• Click on the "File" menu, and select "Open."
• Click on the drop-down box in the bottom right corner that reads "Google Earth."
• Select the option that reads "GPS (*.gpx, *.loc, *.mps)."
• Navigate to the .GPX file using the file browser. Click once to select it, and then click "Open."
• Click "OK" on the data import box, and wait for the import to complete.
• Take all options for; "Create KML Tracks", "Create KML LineStings", "Adjust altitudes to ground height (which is only necessary for mountainous territory)"
• Right-click on the imported place under "Temporary Places." It should read "GPS device" or something similar.
• Select "Save Place As..." from the right-click menu.
• Type a file name, select a location and click "Save." The .KMZ file should be on your computer now.