It looks like something has used silk strands to glue the leaf together ... probably the dark thing with white spots that I can see behind the white strands of silk.

Some caterpillars do this to pupate.

It might also be some insect protecting an egg mass by folding the leaf around it.

It was probably constructed by a Leafroller Caterpillar that never fully completed the job, but nobody at BugGuide has been able to determine exactly what's inside it. I think the white spots are light reflections.