That has the front of a 1969 with the quad headlamps.
Most likely a 1969 although you could put a 69 front on a 70, the only other year it would fit as the 68s and before were smaller and the 71s and newer were a larger body style. While it is uncommon I have seen the fronts swapped between the two years.
The 68s never had quad headlamps, they could have the optional fog lights in the grill but the grill and front was still different from a 1969.
The VIN will tell you as the first digit is the last digit of the year. A "9" will be 1969 and a "0" will be a 1970. The VIN in 1969 and later is on the driver's side of the dash. The first half of the VIN will be interesting as it tells you what the car was originally. If you could get the VIN that would be good and you don't have to post the whole VIN, we just need the first 5 or 6 digits. If the car still has the tag on the drivers door and the VIN (warranty number) matches the dash then get that info too as it will tell you if that is a basic coupe or a Grande, what color originally exterior and interior, estimated build date, what
trans and axle, and area it was sold originally.
How much is it worth?
No way I could even give you a guesstimate with only one long distance photo to look at. There are WAY too many variables with the condition of the car (especially one sitting in a field with tall grass hiding the lower body for who knows how long) and not knowing the options the car has (or had) and what is wrong with the car and why it was left ( abandoned? ) in the yard.
Does someone live there? Can you get in contact with them by knocking on the door or leaving a note on the car. If the place is abondoned or no activity there you can go to the town office and look up who owns the land and contact them. It may be rental property and a previous tenant left the car there and the property owner may just be looking to get rid of it.
I can tell you that coupes do lack behind Sportsroofs (fastbacks) and convertibles in value, even the upscale Grandes. Unless this car is a 390 or a 428 originally it will definitely lag behind the others.
help me indentify my cars year...... 
