If you want to ride offroad on federal lands the bike has to be pedaled to engage the power, not just a throttle. Fed definition of a "bicycle" is less than 700 watts of power (torque power, not battery size) and must be pedaled. Some bikes with throttles are made to temporarily disconnect the throttle so that you can meet that definition. Since you want a "mt. bike" and not just an electric "scooter" (that might handle like a shopping cart or minibike), I would suggest getting one from a local dealer with tech/warranty support. The midmount motors (at the crank) provide the best handling. Bosch, Specialized and Shimano seem to have the best midmount motors. I have a full suspension aluminum Cannondale that works great (didn't have the budget for carbon...that's another $1-2k)...wanted a Specialized but they are $1000+ more than comparable bikes from other brands. I have had three carbon frame mt. bikes...broke the frame on them all (and broke the frame on half the aluminum bikes I've had)...so if you're a heavy hard rider the local warranty support can make all the difference. Carbon definitely rides best...even a carbon handlebar on an aluminum frame really takes the edge off hand vibration. Most bikes come with three power levels...I find the highest power level is not needed if you're used to riding mt. bikes. I ride mine on fairly level roads/trails without any power assist, and then just use the power up hills or against the wind on the way home. Some of the "scooter" type bikes are not geared properly to ride them without any power assist (such as when the battery dies).
