Writer’s Colony–the work of memory

Does anyone have a theory as to why we remember certain things at other times? A snowy afternoon west of Boston and I was flooded with a memory of an autumn thirty years ago–but why? Is the poem the memory or both places together? Does this happen to other people?

***

Writer’s Colony

such a long time ago
on the backsteps
at the MacDowell dining hall
I sat
watching
big moon rise
over the October fields

a woman, about the age
I am now
stopped and asked me
“Are you working?”
and I hadn’t known
that I was
until now.