[edit] The CS route-builder doesn’t warrant the implied shade I tossed at it (below). I’ve now checked more carefully and the two instances where I got “into trouble” could have been avoided in one case (I wasn’t zoomed-in enough to distinguish the foot-trail) and was unavoidable in the other as the source map(s) (OSM?) were inaccurate as to the nature/condition of the road/trail. I’ll leave this post up to see if I’ll get any other route-planning site suggestions. 
I’ve been using the CityStrides route-builder feature to plan walks/hikes for awhile now, and for the most part it works really well. For paved, named city streets, it can’t really be beat.
“Natural”, “off-road”, unpaved situations are a little different. Twice (three times,actually) it’s gotten me “into trouble” in woodsy/hiking areas. The lines indicating “trails” are often the same width whether it’s a “fire road” or scruffy, rutted, overgrown deer trail (essentially).
Los Angeles has a big big urban park (Griffith Park) with a myriad of hiking trails that I’m trying to bag. I’ve ended up on some scary, steep, eroded, slidey foot trails on two different occasions–being ‘fooled’ by the line width on the map.
Not blaming Citystrides–It’s mostly my fault for not researching things more carefully perhaps, but I’m wondering if there’s a more detailed online route-planning/mapping service I could use to lay out a route and export/import a resulting .gpx file for my Garmin watch. Something that might better indicate more precisely the nature of the road/path that might be used.