Emily Brooks is a pseudonym for the authors Penelope Hall and Ann LaFarge. Riding High is a novel aimed at adults, and is set in the 1920s.
Finding the book:findable, but not hugely common. There was a UK printing, but it’s not massively easy to track down.
Links and sources
Many thanks to Lisa Catz for the photograph.
Bibliography - horse books only
Poseidon Press, New York, 1989, 400 pp
Century, London, 1990
Charles "Wirelegs" Manville and Conrad Miles are given graduation gifts of 500 acres of “scrag land" next to both their families' estates in Edgeville, NY. They compete to win the other’s stake - he who jumps the most fences in the next 50 years will win all 1000 acres. 50 years later Wirelegs is terminally ill. His daughter Carlin is unhappy. Conrad is impotent. No one cares about the bet, but they do care about Wirelegs’ will.