Mt. Vaca Loop starts at the corner of Pleasants Valley Rd. and Gates Canyon Rd. The entire trail is on a road that will either be paved/gravel/hard-packed dirt.
PARKING There is a gravel area at the street corner with enough room to park about 6 cars and an area on the other side of Gates Canyon where a couple more cars can park.
DISCRIPTION From the parking area you head up Gates Canyon Rd which starts out as a paved road then turns into gravel with some sections of hard-packed dirt. This road leads you to Blue Ridge Rd which will take you past all the antenna's and the summit of Mt. Vaca itself. This road will lead you to Mix Canyon Rd which takes you down to Pleasants Valley Rd. The last 2 miles are on Pleasants Valley Rd and it leads you back to the parking area. It is very difficult to get lost on this route as the roads lead into each other pretty well. There is one section where there is a "Y" in the road near the summit. The route that hits the summit goes left and is depicted in the GPX that I attached. The route on All Trails has you go right and bypass the summit for some reason:(
TRAFFIC The only traffic that you will encounter is on Pleasants Valley Rd. It is a relatively busy road, but there is a descent sized shoulder and everyone is respectful (that I encountered) and pull over to give you some space. On Gates Canyon, Blue Ridge, and Mix Canyon you may see a jeep or two and a motorcycle.
STRAVA There is a Segment on Strava and the current CR (11/9/2021) is by Tommy Vargas with a time of 1:36:45 on May 30, 2019.