Ken,
Yes, it was called both "Diamond Grove" and "Picnic Grove." The site where the 6th Kansas was camped on Massard Prairie was a large grove of trees with a little stream flowing through. It was a popular picnic and preaching site before and after the war. The name Diamond Grove is used in quite a few of the Texas eyewitness accounts.
I should mention about the book that all profits are being donated to historic preservation efforts in the area. 50% will go to the new Cane Hill Battlefield Driving Tour project. If anyone is involved with or knows of other projects in the area that could use a portion of the proceeds, please let me know.
It is available through my website now at www.exploresouthernhistory.com/massardprairie and will start popping up on all the standard online bookstores in about 2 weeks. The Prairie Grove Battlefield State Park Gift Shop will have them in 7-10 days and other locations should be available soon.
Best,
Dale