Well, wish I had a better report to offer using the small coil on the F-75. Most of the items recovered were old round pull tabs, various pieces of small flat metal and two (2) old type square nails. Did find a few corroded clad cents but no silver. Small coil worked great in and around the tall weeds and tumbleweeds.
Had a chance to talk with a park employee (ranger?) and assured him that they would find no trace of my digging. He said that was all they cared about. Mentioned the lack of good targets and he pointed out that the highway (I-25) train overpass nearby would have taken a lot of fill to build up the berm for the highway to pass over the tracks. He noted that typically the fill comes from adjacent land and that the top foot of the area I was hunting may have been taken for the highway overpass. Makes sense except for the square nails. I'm not done with that area just yet.
Although most of the time was spent in 2F, with occasional 4H, I tried Nasa Tom's favorite; tone 1, Disc. 6 for a short time just before I quit. I must admit that I kinda like the 1 tone because good targets give a solid tone and iron is short and sputtery. Stayed with it for around 3 1/2 hours and the F-75 with the small coil was very kind to my shoulders. I dug an awful lot of targets, including some I shouldn't have, just to learn. The Ground Shark saved the day for me.
Ron