In 1900, John B. Slater, an attorney, was living with his wife Florence E. Slater and a number of relatives, including son Ronald, in Colville town, Stevens County, Washington: John B. Slater, 40 b. California April 1860; Florence E., 39 b. Oregon April 1861; son Ronald B., 9 b. WA Sept 1891; and several relatives? named Wright. John's father was born in Ohio and his mother in Missouri; Florence's parents were born in Indiana. They have been married for 10 years, and Florence has had 1 child.("United States Census, 1900," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MMPB-KW6 : accessed 30 May 2016), John B Slater, Colville, Clugston, Meyers Falls, Old Dominion, White Lake, and Marcus Precincts Colville town, Stevens, Washington, United States; citing ED 75, sheet 20A, family 332, NARA microfilm publication T623 (Washington, D.C.: National Archives and Records Administration, n.d.); FHL microfilm 1,241,752.)
In 1880, John B. Slater, a 20 year old laborer b. CA, was living with his father, James Slater, a 55 year old laborer b. Ohio, in Prineville, Wasco, Oregon. His brother, William P. Slater, 18 b. Oregon, also lived with them. John and William's mother was born in Missouri. James Slater's father was born in Virginia and his mother in Pennsylvania.("United States Census, 1880," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MNC5-25D : accessed 30 May 2016), John B Slater in household of James Slater, Prineville, Wasco, Oregon, United States; citing enumeration district ED 125, sheet 299B, NARA microfilm publication T9 (Washington D.C.: National Archives and Records Administration, n.d.), roll 1084; FHL microfilm 1,255,084.)
Here is a link to a biography for John Berry Slater published in N.N. Durham's ''Spokane and the Inland Empire; and Spokane County Washington,'' 1912?, Vol. 2, Pages 28-29
John's parents, James Slater and Sarah Jane James, were married in 1859 in Linn County, Oregon.(Oregon Secretary of State; Oregon Historical Records Index (http://genealogy.state.or.us/detail.php?id=38311)'
The FindAGrave memorial for John Berry Slater says that he died on 28 Nov 1928 in Alameda County, CA, and was buried in the Fairmount Memorial Park, Spokane, Spokane, Washington. The memorial includes a picture of him.(FindAGrave.com; Created by: Ronald Slater; Record added: Aug 04, 2015; Find A Grave Memorial# 150201621 (http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=150201621)) The California Death Index shows that he died on 29 Nov 1928.("California Death Index, 1905-1939," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:QKSM-DFBK : accessed 30 May 2016), John B Slater, 29 Nov 1928; citing 54541, Department of Health Services, Vital Statistics Department, Sacramento. Certificate #54541).