Theme: Approaches to Skyline Rim

Duration: 13:34-17:38 (4 hours 4 minutes)

Participants: Digby Tarvin, Bob McNally , Louise Wynn

Equipment: ATVs, GPS, Camera, Scintillometer, magnetic susceptability meter, printed route maps, compass

Route:

• 0518.17E , 4250.93N (Hab)
  
• to wpt 110 (0518.35E, 4251.14N)
  
• to wpt 111 (0517.75E, 4251.54N)
  
• to repeater location (0517.94E, 4250.90N)
  
• to wpt 111 above
  
• to wpt 112 (0517.13E, 4251.32N)
  
• to wpt 113 (0516.06E, 4251.39N)
  
• to wpt 114 (0515.37E, 4251.43N)
  
• to wpt 115 (0514.93E, 4252.20N)
  
• to wpt 116 (05115.26E, 4252.56N)
  
• to location (0515.65E, 4252.83N)
  
• to wpt 113 above
  
• to wpt 112 above
  
• to wpt 111 above
  
• to wpt 110 above
  
• to wpt Hab above

Objectives/Work Done: This EVA was conducted to evaluate approaches to the base of Skyline Rim, points north, and also to check the location of the repeater radio transmitter on the ridge overlooking the Hab. The opportunity was taken along the way, to take geophysical readings and photographs. The crew rode up onto Hab Ridge, and headed south at wpt 111 for 500 meters to locate the repeater radio. We found the repeater station over-looking the Hab, and noted its location as a rainsquall swept in from the southwest. We returned to wpt 111 and struck out across the plain, following existing ATV tracks where possible. Near 111, we found the ground covered with vast numbers of fossil oyster shells of a type previously identified by our geologist as late Jurassic, from the Dakota formation. We reached the base of Skyline rim approx 14:20.

We explored along the base, looking for easy access up to the cliff base for future geological work. The cliff base was obstructed by tall, steep piles of talus, which consisted of soft dirt. The ATVs easily bogged down in the soft semi-muddy soil, restricting how close we could get to the cliff. At one point an ATV was dug in up to its rear axle in soft soil on a steep uphill. We freed it by digging out behind the rear wheels and walking alongside it with the ATV in reverse, and a little throttle applied.

We made photos and marked waypoints for future reference. We continued to work north, paralleling the cliff base, and found that the long alluvial fans deposited below the cliffs, greatly impeded our progress. Steep ridges of very loose, dark soil alternated with steep gullies. We crossed 3 or 4 of these, and could see many more along our planned route. These features did not appear on our topo map which has 40 foot intervals between contour lines; many of these features were less than 30 feet high, but they were steep enough to greatly slow us down, picking our way through them. We turned southwest for the firmer tan soil of the plain, and our route back to the Hab at about 16:39. We followed waypoints and ATV tracks back to 111, and then back to the Hab.

Weather: Cloudy and rain showers. Temp 45 deg F

Maximum distance from Hab: 3.14 km

Lessons Learned: On flat terrain, Cross country travel can be conducted in straight lines between waypoints a lot of the time, with minimal detours. Close to heavily eroded cliffs, the alluvial hills and gullies make straight forward progress impossible, requiring many detours. Features that are too small to really show on the topo map can still be big enough to impede progress. Small, printed route maps with bold waypoint and route lines drawn in, help field navigation a lot, especially when detours are necessary. GPS units are so sensitive to motion that simply picking one up from its storage place in pocket or on the ATV changes your apparent track, so a compass is still a very useful tool for maintaining orientation.