Felicia Moon, 55, and James Thomas, 50, were arrested and charged with misdemeanor public lewdness Monday, KHOU-TV, Houston, reported.
The trail-riders were making their way from Prairie View to Memorial Park, an annual event leading up to the Houston Livestock Show and Rodeo, the TV station said.
"I don't see it as [a] big deal," trail boss Nannie Francies told KHOU-TV Tuesday. "When people go out on the trail, people tend to do what they want to do."
The Waller County Sheriff's Office said the pair were free after posting $500 bail.