Greg, it's a 10 hour bus ride from Bogota on pretty decent roads. Getting there from Popayan is quicker, but its over the mountains on un-sealed precipitous roads. besides Popayan is on many foreign government's DO NOT TRAVEL list.
San Augustin is deep in the heart of what once was notorious guerilla territory, its less overtly dangerous these days, but travelling at night is not recommended.
Some of the jeep tour operators around town get a bit light fingered around valuables.
But there are so many tourists who go to visit the UNESCO heritage site these days that, within reason, its ok.
we have a few more Colombia travel tps on the safety Hub
Phil about 6 years ago