Yesterday, before winter hit with a vengeance, I had a chance to take a [perfect] day for some field work in the lower Colorado River area. An awesome day to say the least. Hiked 10 miles in 9.3 hours. Recorded entire traverse with GPS and took many pictures. Used the GPS to record tracklog in gpx form. Used that to geotag my photos and to create an archive of the traverse. Our goal on this day was to field-check outcrops that we had identified as possible variants of a key geologic unit that we often pursue along the lower Colorado...the Bouse Formation. It is a conspicuous white marl with associated muds, sands, tufa, and gravel. It records an important interval in the origin of this course of the river.
We used Google Earth to perform a 'virtual' reconaissance of our study area. Very good imagery is available, and that makes this part pretty easy. We flagged all of the plausible outcrops of the Bouse formation in an area of interest, printed out the map, and then hit the field for a long hike to see which ones were correctly identified. The unit has a known elevation range (based on our previous work in this valley) so the reconn. can be focused. For example, there is a contour line on the image that denotes the upper limit of the unit in the landscape.
Following the traverse, we used and updated various symbols to indicate yes, no, and ambiguous based on our field work. The attached image shows the traverse, its topographic profile and various measures of distance, altitude, and velocity. Also shown are the geotagged photos that were taken on the hike. The blue symbols denote areas we have already been to verify the existence of exposures of the Bouse Formation. Each placemark has some meaning (yes, no, or maybe) and can be accompanied by explanatory text.
Of note. The virtual reconnaissance with Google Earth was extremely helpful, it narrowed down our quest tremendously. We also learned the obvious lesson (that we have learned so many other times) that just because there is a blob of white in the image at the right location, it doesn't mean it is the white unit you are looking for. Also, during the hike, we found some outcrops in extremely narrow, steep-sided (slot) canyons. These outcrops are only evident from field work. Image interpretation for geologic mapping is immensely useful, but never precludes field work.
The profile shows a novel correspondence between topography and my hiking pace (the red is topography, the blue is velocity). It also reveals areas where I stopped to collect samples, take notes, photos, eat, or rest. Download it and you can actually 'play' it and watch it develop as it did in the field that day (see also:
http://geologicfroth.com/finessing-traverses-with-topofusion-and-googl). If the profile included the transit of the sun, you would see that the last 2 miles or so of the hike were in near to complete darkness. Always take a headlamp in the field...trust me. Without one, we would have been boned.
Here is a link to the photo album which can easily be opened up in GE:
The gpx file of the traverse is also attached as a kml file. The traverse, the field points, the photos, and other ancillary information can all be saved in a single kml file to archive the day's effort. I do this all the time and have posted several examples. Why wouldn't you do this? It is so freaking obvious.
