Asked June 04, 2020, 3:31 PM EDT
Delta County Colorado
It sounds as if you have a type of slime mold, which is fairly common on wood chip mulch after a couple of days of rain. Once considered an animal because of its creeping nature, this mold is really a fungus. Slime mold dries into hardened structures that produce dark masses of spore like bodies and clouds of dust like particles when broken apart. The spores are spread by wind, water, mowers or other equipment.
Slime molds are more a curiosity or nuisance than a threat to gardens or lawns. Once a colony starts to form, allow mulch to dry out, or use a garden or leaf rake to break up the colony and provide control. You also can use a shovel to remove and dispose of it. Slime mold should be enjoyed as one of natures oddities. https://planttalk.colostate.edu/topics/insects-diseases/1435-slime-mold/
I would monitor your watering. If you dry out the soil 2-4" depth, and then water, that will help get rid of it. You may also have too much organic matter in your vegetable garden so mother nature is working to break it down. I would fertilize with a nitrogen fertilizer as well as this breakdown process can tie up the nitrogen. https://extension.colostate.edu/topic-areas/yard-garden/fertilizing-the-vegetable-garden-7-611/