Mullins said he timed Castledale in 1:11 flat.
In his only start on dirt, Castledale finished sixth in the March 6 San Rafael Stakes (gr. II).
"We've watched him work on turf and we've watched him work on dirt," Mullins said. "He just moves so much better on the dirt. He's really impressive on the dirt so we think he's entitled to another shot at it."
Castledale, a bay son of Peintre Celebre and Louju (by Silver Hawk) is owned by the partnership of Greg Knee and TVG racing expert Frank Lyons. The Irish-bred won one of seven starts in Ireland before being imported to America late last year, where he won the Generous in his first start stateside. From nine career starts, he's won twice with two seconds and a third for earnings of $109,623.