John Eva Bartle would have been 28 in 1850, his wifes name was Nannie T. Grenfell, they would have had 1 or 2 children in 1850.
I suspect that the John e. Bartle that you mentioned in the Calif. 1850 census is my ancestor for a couple of reasons.First, the middle initial and age etc arecorrect; I know that he went to CA in 1850.Also, at the same census location there is a John T. Grenfell listed, whom I think is brother-in-law.
A couple of other items.
In a book entitled "The Famine Immigrants" vol 5, p 471 - "John Bartle, age 20, a Farmer, arrived NY Aug. 10, 1849, on ship Marmion from Liverpool".
In "Gold Rush Days, Misc. Records 1856- 1862", Vol 3 p 7 "10-7-1856 Bartle, John, unclaimed letter, Stockton P.O."