I took a look through Butterfield's Double Mirror and am not quite sure.
I got the impression that Butterfield mostly spent time at Trungpa's center in Vermont, which was first named Vajradatu (Tail of the Tiger)
and is now Karme Choling.
Trungpa was cremated there, and some of what Butterfield writes sounds
as though he was there, doing doing his own ngondro practice, at that time.
[www.google.com]
I got the impression that Butterfield mostly spent time at Trungpa's center in Vermont, which was first named Vajradatu (Tail of the Tiger)
and is now Karme Choling.
Trungpa was cremated there, and some of what Butterfield writes sounds
as though he was there, doing doing his own ngondro practice, at that time.
[www.google.com]