This road was recommended by Chris from automotive.com, so a big thanks to him.
Glendora Mountain Road (running into Glendora Ridge Road) goes from Glendora through the Glendora Wilderness Park and all the way up to Mt. Baldy. It is located in the mountains just above the 210 Freeway and is well worth the trip to get there.
To get there is to exit the 210 at Grand, head North to Downtown where you will turn right at Foothill, left on Valley Center and then another left on Sierre Madre - and your run can commence.
As you can see from the video below, this road is mostly a single lane, but quite wide and has good quality pavement which will make your drive nice and smooth.
One thing to remember, though this road is not used much by cars it is used by cyclists, bikers and runners, so be carefull. When you encounter a blind bend, stay on your side of the road.
Glendora Mountain Road
Total Miles: 21
Driving Time: 45 Minutes
After about 12 miles you will come to a fork in the road and you can chose if you want to continue along Glendora Mountain Road or take Glendora Ridge Road upto Mt. Baldy - the choice is yours and both are good options.