Scavenging, is one of the most annoying things on my list at the moment.
I spent literally 35minutes to find the four resources on a Scrap Mound. Harvested the four Scrap Cloths and had not only the Cloth resource disappear, but two other Scrap resources as well.
This seems unfair. When the other resources aren't being gathered, and it hasn't 'turned to rock', it would seem likely to leave the other resources available to be gathered.
After all to get all four scrap resources on the same part of the pile, takes a while (if at all) to find.