Ruth Armer (May 26, 1896-August 29, 1977) was an American abstractionist painter, lithographer, teacher, and art collector from the San Francisco Bay area in California.
Biography on Wikipedia: https://en.wikipedia.org/wiki/Ruth_Armer

Abstraction #250 by Ruth Armer
c.1950 / Oil on canvas / 24″x20″ / Private collection

Ruth Armer on Artnet: http://www.artnet.com/artists/ruth-armer/

Further reading:
https://helfenfinearts.com/ruth-armer/
https://calabigallery.com/artists/ruth-armer/
http://womenoutwest.blogspot.com/2014/03/ruth-armer-from-representational-to.html