Is it safe to hike this trail alone on a weekend late afternoon?

I would bring pepper spray if you're going alone. Just to be safe :)

I'm not really sure but you have to look out for mountain lions and bears

No need for pepper spray. That is pure paranoia. Nor is there any concern for lions & bears. Those comments are way out of line. From Ridgewood park west the trail is relatively flat save for a few shallow ups and downs. The dirt trail comes up to Black Mtn. Rd. Where you'll need to cross to pick up the trail by going under the road by way of the trail connector just to the south at the Canyon Side Ranch or cross at Mercy Rd. (a bit further south along Black Mtn. Rd.) From there the wide trail continues west all the way to the ocean. There are s series of single track side trails north of the main wide trail that are quieter and can provide somewhat more shade on hot days.