I recently read a book on building of the Owens Valley aqueduct to Los Angeles. The chief engineer bought 28 Holts to try to replace mules. He gave up on them. Said buying them was one of his big mistakes. One section of steel pipe he had to move across sandy desert was 26 tons and took a team of 52 mules to pull it on a cart with wheels that were 24 inch wide. Don't know what models were made then but one picture looked like they were gas powered engines and not steam.