The most common routes I've taken to the North Ogden Shoreline Trail is from the North Ogden Pass directly onto the trail, or from the end of 3550 North (the east end) taking steep trail that connects up to it. On this particular ride we turned north just before the church on 3550, and rode the rodes up all the way to the highest street, Nebo Ave, where you turn left and then look carefully on the right for a faint trail that is much shorter and less steep that connects to Shoreline.
This ride we actually didn't really ride Shoreline, except to cross over it, and went straight from this connector trail (where the first two pictures are from) to what I will call the Mason Cove Trail, until I hear its actual name. You actually keep riding up the Shoreline Trail by the powerlines until you come to an empty retaining pond, ride around that until you see the trail heading into the forest, without any trailhead or signs. This is the new one that I started riding a year ago that is not quite finished, although everytime I ride the trail it is a bit longer.
Mason Cove is a beautiful trail, with lots of winding through forested sections, occasionally popping out on rock slides with great views over the Ogden valley. I highly recommend the trail. It is not too strenuous aerobically, although it is fairly technical. It is fairly short right now, although if you decide to add the loop that splits off right on the way back down you get some decent length and good climbing on it.