This would be the third of five attempted confluence visits on a trip to Colorado and back. I was on my way from Creede, CO where I had been researching the feasibility of visiting 38N-107W and had just successfully visited 39N-106W the day before and had gotten quite muddy.
I would meet up with Sam Gallucci for a joint visit. This confluence is near a recreation area of my alma mater and the smell of the trees brought back a lot of memories.
I met Sam and we were able to park within a kilometer west of the confluence along Loy Creek Road. There was a hint of rain to follow up an earlier snow flurry with large flakes! It only took 21 minutes over mostly open terrain to find the confluence . There was a small beaver pond and stream to the west that had presented a minor challenge and detour into the trees south of the point. Sam had brought an Ashtech Z-Xtreme survey grade dual-frequency GPS unit and antenna and I would be using my Trimble GeoXT (L1 only), to document our visit.
This confluence is located on a south facing slope north of a northwest-southeast running trail on upsloping terrain halfway between a large double pine tree and the trail. There were 2 small dead trees to the right and a cluster of 4 trees to the west: 2 single ones and another double pine tree with trunks split into a “V” shape. If you were to visualize a triangle with the hypotenuse between the two double trees and the long side parallel to the trail, the confluence would be at the right angle intersection. Behind you, and on the other side of the trail, would be some aspen trees.
Post processing and differential correction of the data from the GeoXT at two slightly different positions (WGS-84)
N38 59 59.96899
W104 59 59.93035
2816.424m (MSL - EGM96)
Horizontal Precision of 1.2 meters with 1998 positions
The second position resolved to the following:
N39 00 00.01990
W104 59 59.92943
2815.910m (MSL - EGM96)
Horizontal Precision of .8 meters with 101 positions
After fumbling around with a survey-grade GPS unit, Sam inadvertently recorded 97 epochs in raw data. He processed them using 2 Denver CORS. With a 0.5-foot accuracy, the confluence was S 78° 31' 12.50740" W a distance of 7.964 feet from the antenna position. Not where he expected it.
Here's the resolved position:
Lat: 39° 00' 00.01566" N 95% Error: 0.435
Long: 104° 59' 59.90118" W 95% Error: 0.477
Height: 9211.841 US feet 95% Error: 0.514
Picture 1 looks west. Picture 2 looks north. Picture 3 looks east. Picture 4 looks south. Picture 5 shows our GPS position. Picture 6 shows the GPS units used to locate the site. Picture 7 also shows our GPS equipment.
What a great confluence adventure and dry run for our survey-grade GPS visit to 38N-107W!