Nice to learn of a new "cousin"! I suppose we ought to put this in to the Stewart subject as I don't think our line had any relationship to poor Mr. Leonard I Smith.
However, to answer you. I first learned of the cause of Benjamin's death from the "History of Tooele County", by the Daughters of the Utah Pioneers, published in 1961 by the Transcript Bulletin Publishing Co., Tooele, UT.
It has brief biographies of many of the early pioneers to Tooele County and Benjamin's is included. In it, is stated: Benjamin Thomson Stewart was born September 26, 1826 or 1827 in Glasgow, Lanark, Scotland, the son of James Stewart and Margaret Cassels. On January 12, 1850, he married Agnes Gillespie. They were parents of eleven children. Within a year after their marriage they started the long trip to Zion. They crossed the plains in 1853 with Capt. Moses Clawson's Company. They settled at Tooele where they lived the remainder of their lives and reared their family. He had a little farm west of Tooele where he made a meager living, but after Johnston's Army came to Utah in 1857 he turned his farm into a truck garden and supplied the Camp with produce. After the army moved, he sold his vegetables and fruits to the miners at Stockton for many years. When he failed to return from a trip on August 10, 1877, Agnes became worried and sent friends to look for him. He was found dead under his wagon in the bottom of the gully at Soldier's Bridge. It was assumed that his horses had become frightened and run away, overturning the wagon.
- Dora Stewart Allen as told her by James Lawrence Stewart."
I have some other info on Benjamin and will be happy to share. I am descended from their daughter Martha, born in Tooele in 1855, how about you?
Look forward to hearing from you.