The trailhead is basically the summit of Marshall Pass. Just on the east side of the pass, less than .2 mile down, there's a fairly large parking area where the road curves back from the north to the east. This is used primarily to access the shared Continental Divide & Colorado Trail and for ATV's. To get there from Gunnison, drive east on US50 to Sargents and turn right (SE) onto the Marshall Pass Road (CR243) which further up is FR243 and rated passable for passenger cars. At a major intersection about 5 miles in, be sure and stay right and continue on 243 to the pass which is about 16.5 long miles total. This road follows an old railroad bed so it never climbs steeply and to gain elevation, it seemingly winds all around to gain the pass.
If coming from the Front Range, find you way to Poncha Springs where US285 and US50 intersect. Continue south on US285 and turn off to the right (SW) onto CR200 at Mears Junction (also labeled the Marshall Pass Road). If you have come to the summit of Poncha Pass, you've missed the turnoff. Turn around and go back about 2.4 miles. Follow the old railroad bed all the way to Marshall Pass. About 2.4 miles in, you'll need to make a right turn and less than a mile further, another right at a four-way junction in order to continue on course & FR200 to O'Haver Lake and eventually Marshall Pass. It's a little over 14 miles from the highway. To reach the actual pass summit, you would have just driven by the parking area mentioned above. CR200 is also rated passable for passenger cars as well.