Mrs. E.J. Rockwood had been living in Castle Creek, a hamlet north of Binghamton in south-central New York State.

https://en.wikipedia.org/wiki/Castle_Creek,_New_York

At Christmas of 1919, however, a postcard greeting to Mrs. Rockwood was forwarded to Southwick, Massachusetts.

Southwick, a town in the Connecticut River Valley, adjoins the border of Connecticut in south central Massachusetts.

https://en.wikipedia.org/wiki/Southwick,_Massachusetts

We cannot tell if Mrs. Rockwood had moved, or was enjoying an extended holiday visit.

It appears that the postmaster inscribed the forwarding address.

The Christmas postcard was mailed from San Diego, California, on December 17. 

The face bears a small medallion illustration of Bridal Veil Falls and a verse lauding the natural beauty of Yosemite.

Published by the M. Kashower Company of Los Angeles, the postcard does not identify a particular postcard illustrator.

The concluding lines of the verse describe the postcard as “a Christmas salute from the West to the East.”

One can find numerous examples of Christmas postcards bearing pictures of the warm-weather flowers and fruit of California that were mailed to correspondents in the East and Midwest – who ordinarily experienced cold weather and snow in December.

Mrs. Rockwood seems to have appreciated the postcard from her friend who inscribed only initials; the greeting was preserved in good condition for a century.