OMG.. You are one lucky man ive found one in 35 years and was with someone who found another one 5' from me. its the top prize for a collector in my opinion. Its a full groove axe head no telling how old it is as native americans been making them for thousands of years. The only way you may put a date to it is by finding other artifacts that may be on the same site like pottery sherds or arrowheads as they can be dated by the style. Even then you will really never know as a native may have found it himself. Would love to see it in person someday..Congrats on a great find.