From the locked gate, you will have to drive another two miles with your guide on a 4WD road to the trailhead parking area next to the old Ortiz Mine. The trailhead is at an elevation of about 7,200'. If you don't have a 4WD vehicle, you can leave your car at Goldmine Road and carpool with someone else who has one. From the trailhead, a 2-mile long trail takes you all the way to the summit of Placer Mountain. The trail is faint and brushy in places, but you will just follow the guide.
A PDF trail map is attached below. Click on the red X, then click on it again to view the map.