With the female's pulling not getting her anywhere she started rolling in place to get the little male off of her.  A few more minutes of this and he did let go.  It was approximately ten minutes or so after initial copulation that the pair split up. I checked both snakes afterwards, thegreen snake was no worse for wear. The red one had what seemed to me a visible sperm plug. I don't know if Garter Snakes are known to produce such a thing, but the red snake's vent was filled with a translucent gel that seemed like it would be tough to the touch. (I refrained from doing so.)

    Once the whole thing was over the snakes went their two different ways.  We saw two or three dozen individual snakes that day, although only these two were observed mating.  After emergence the snakes all disperse to their home ranges, some of which may be as many as two miles away.  Come winter they will converge again on this same spot and it will all start again.