Let's give this a go, since people are already starting to sign up. I'm no Google Maps expert, but I was able to pull in a gpx I have of the Southies, and add a new pin at the underpass at Williamson Creek and Brodie. The photo I tested with is not of that spot, btw.
https://www.google.com/maps/d/edit?mid=1nR_plAj1uMxeI7XoA_Im3bR0-_F1gwY8&usp=sharing
Can others see and add to this map? Maybe add your user name if you are volunteering for a particular spot?