These two letters were purchased from the Zane Grey estate held at Lang's Auction, October, 2007.  Both are from about the same time period.  Both are from Lina Grey to her son Romer.  Following is some of what's in the letters:

The first letter is with envelope with date stamp of December 3, 1951.  His Mother mentions that Romer's son paid her a visit and drove her into LA to see movie Que Vadis,and celebrated his Birthday.  She also talks about giving up "this place" Altadena Home, as the stairs and all were too much for her. So, she bought a home!  Offers the Altadena home to Romer until its sold. 

Second letter does not have an envelope and is undated, but seems to be about the same time period as the first one.  Romer's son paid a visit with 3 pals.  The family dog had 4 pups, daughter Betty slept nearby on an air-mattress until "The blessed event".  Walter Black continues tremendous ad campaign (on the Gruber books I believe?).