You need fiber optics ran between these sites. If you ran copper or ethernet you would have to put repeaters in between the sites..
<b>There are many options…</b>
The Best is to bury a fiber cable between the sites. (10 gig is max speed)
The next best is to bury Copper between the sites or see if you can get two “dry pairs” from the phone company and use an ethernet extender like what TUT Systems sell. Keep in mind they have a 1500 ft limit. (75+ mb is max reliable speed. It is less as the distance increases)
The acceptable option is wireless. This will only work well if you have a clear line of sight. (I reccomend 3Com bridges for this) (54mb max <b>Note</b> there is talk of N bridges but they currently have limits on distance.)
The last option is Leased DSL or T1 (T3) lines. These are usually very reliable but are very exspensive and slow for the cost.