Potomac — Hundreds of horses and riders, including at least one rider headed to London on the shortlist for the Olympics — Allison Springer — converged at Bittersweet Field this weekend, June 16-17, for the Seneca Valley Pony Club Horse Trials. Each horse-rider combination competed at one of six levels of difficulty in dressage, stadium jumping and cross country jumping. Jumps ranged from about 2.5 feet to nearly 4 feet in height, with a variety of challenges like ditches, banks and water.