This is a significant variant of the regular East Slope route, and is, according to Secor, "more scenic, but much more tiring than the eastern hanging valley." I'm not sure how it can be more tiring, it's a half mile shorter than the regular East Slope, and the starting point is the same, making for the same elevation gain either way. Just the same, I would agree that it is much more scenic, with views across to Laurel Mountain, and close-up views of Torre de Miedra and the North Buttress.
From the boat ramp at Convict Lake, take the trail to the left that contours the east side of the lake. Stay on the trail longer than you think you should, until you enter the thick aspens at the southwest end of the lake. When you find yourself walking on a little causeway, delineated by rows of rocks on both sides, look for a use trail to the left. This trail will save much bushwhacking, it parallels a grove of slide alders, and then makes an end-around to bypass the alders. If you find yourself fighting the brush, backtrack and find the trail again. It is much easier and more pleasant to stay on this use trail. Initially, it may seem to be going the wrong way, but once you make the end-around, you are headed for the peak.
From the edge of the slide alder barrier, head up through the sagebrush on well-used game trails, aiming for the notch that is the low point for the hanging valley above.
Head up the hanging valley, passing Torre de Miedra, a light colored rock buttress, on its left. This valley is full of talus, but it's mostly the good kind, it doesn't move when you step on it.
Shortly after passing Torre de Miedra, you will pass the North Buttress of Morrison itself, a spectacularly loose cliff, which is the face that you see from Hwy 395. Continue on to the head of the valley, and here you will join the regular East Slope route. Just before you reach the valley head, resist the temptation to take a steep chute that branches right. It looks like a short-cut, but it dead-ends in a loose cliff band.
Ascend the ridge at the top of the hanging valley on a use trail, and when the climbing gets to be steep, traverse right above some exposure (you'll be above the dead-end chute that you passed on the way up to the ridge), and follow one of the well-traveled chutes leading upward.
After a couple hundred yards, a right turn becomes evident, and soon after this turn you are on top.
Comfortable shoes, some water, that's about it. Approach-type shoes with sticky rubber soles will offer the opportunity to pick a sportier route after the ridge is gained.
A little history...
Mt. Morrison is sometimes called the "Eiger of the Sierra", notorious for its loose rock, especially on the North Buttress. But all of the routes have some loose rock, and the Northwest Ridge has more than its fair share. The Northwest Ridge was first climbed by Norman Clyde (who seemingly had 1st ascents on about 90% of the Sierra peaks) in 1928. This route, unlike the East Slope, is not often attempted. As a note of interest, Glen Plake, (in)famous extreme skier, has many winter and spring ski descents of the peak.
More info, courtesy of Diggler. It was interesting how Clyde decided to climb Morrison - John Mendenhall (another prolific early Sierra hardman), after staring up at Morrison so often while on camping trips with his parents at Convict Lake, asked Clyde (probably the most knowledgeable source around) if Mt. Morrison had seen a first ascent (John being interested himself, I'd suspect)- Clyde subsequently hopped in his car, drove to Convict Lake, and made the peak's first ascent. Mendenhall said he kept his plans secret after that.