I think this discuession has been made in the past. You will need a mountian bike or off-road (all wheel drive) vechicle. As for the freeway I have been told it is legal to ride your bike on the freeway from the stretch by the gas station to the next off ramp by the trains (1 mile), from there you are back on surface streets. A better option if you have the legs is have someone drop you off at Encanto and ride up 39 to 2 and then come back the way you suggested. If you do the loop (with out being dropped off) that will be around 100 miles and 10,000ft.