A couple of items for you: 1. Lillie/Lily K. Harriman and husband, Clark S. Harriman, divorced in 1897 in El Paso County, Colorado and Lillie/Lily shortly thereafter married John Mortimer - so Sidney R. Harriman, born 1902, appears to be the son of Clark S. and his subsequent wife, Inez M. Groves. Clark and Inez state in the 1910 census that they have been married 10 years, so it makes sense that Inez Groves was Sidney's mother. That makes your grandfather, Frank W. Harriman, a half-brother to Sidney R. Harriman - Frank's father was Clark and his mother was Lillie/Lily K. Sanborn.
2. Sidney R. Harriman died in 1990 (you will find him in the SSDI) and is buried in Mesa County, Colorado.
I was pleased to have Mary Eleanor's maiden name of Brown. Can you tell me your source for that? I see that you also know Sidney's middle name was Radcliff - can I have your source for that too? Both items may simply be "family papers" or personal knowledge, which is fine, but I'd like to cite you and your source in the HFA (Harriman Family Association) database.
Thanks for the info! I see that you submitted info to the HFA in 2008 - thanks for that too! It all helps.