A less common way to ascend Hastings Peak is via the ridge that separates Hastings Canyon from Bailey Canyon. Routefinding is much easier if you go up this way rather than down, and that's how I've described it here.
Take the 210 freeway to the Baldwin exit, go north to Carter, and then west to Bailey Canyon Park.
Start up the Bailey Canyon Trail from the Bailey Canyon Park in Sierra Madre. About 100 meters north of the Passionist monastery, go west into the flat area north of the monastery, and then ascend the ridge via a use trail. This brings you to a 2100' hill, beyond which is a saddle that looks scary from a distance. Once you get to the saddle, you will see that there is straightforward class 2 way up, with good hand- and footholds, although you do need to be careful of the infamously crumbly San Gabriel rock. After this, there is some more steep stuff, and then a gentler grade leading to the place where two big ridges unite: the ridge separating Bailey Canyon From Hastings Canyon, and the one separating Hastings from Pasadena Glen. Continue up to the triangulation station at 4050'. All that's left is a short hike northwest to Hastings Peak.
Coming down this ridge, the routefinding is much more difficult, and I would recommend simply descending by some other route. At 2600', the ridge splits up into five ridgelets. The one you want is low and nearly invisible. The other four cliff out. Follow the use trail through some tall bushes. You're on the right ridge if you pass through UTM (NAD27) coordinates 0402004, 3782669 at 2454'. From this point, you should see the northern lip of the saddle at a bearing of 210 degrees clockwise from north. Sunnyside Ave and the monastery are useful visual reference points.
The usual essentials for the San Gabriel front range.