Taphrina deformans is a gall causing fungus that infects the leaves of Prunus species, especially Peach and Nectarine, but also Almond, Apricot and some other ornamental Prunus.  The leaf blade and veins are distorted and thickened, and are bright red in summer.

On Cherries, Taphrina weisneri can cause similar galls on leaves.

host

Photograph the gall on the host; ensure you have noted the host species in your comments