I have 35 Clark entries in my book "Iowa Connections" but I picked out these 4 bearing names you mention:

CLARK, BENJAMIN (Captain)
Came from Virginia to settle his claim in Muscatine, Muscatine Co., Iowa in the 1830''s. I believe he was also the first man to settle Buffalo, Scott Co.. His son, David H.,born 4/21/1834, was the first white child born in that county.

CLARK, BENJAMIN
Died in Grundy Co., Iowa in 1875.

CLARK, GEORGE A.
Buried in the Clark family plot of Bloomfield, Cemetery, in Davis Co., Iowa.. Born 1869 / died 1914.

CLARK, G.W.
Was one of the founders of Fostoria, Clay Co., Iowa.

More information: George was born about 1850 in Ozark Missouri, or close by. He married a gal named Belle, no other information. His children's names, Hirem, Wilbur, FLorence, Benjamin (Frank) Minor, and Cora.
George & family lived in Mills County, Iowa, on St. Mary's Island, until it flooded.
He took off one spring to lead some wagons west and never returned.
Frank married Mary Victoria Kaiser in 1889. They had; Roy, Maurice, Florence, Margaret, Leonard.
I can't find them before the 1900 census. Frank & Mary show up, with no children. They lived in Bellevue, Sarpy, Nebraska from 1900 on.
Any help would be greatfuly appreciated.
I'm really thinking he may of changed his name a little for some unknown reason. lol