Dirty, bumpy stuff stuck to squash?
What you see: Corky, bumpy, light brown stuff on the surface of the squash. It may look like dirt, but it won’t wash off. What it is: Healed over areas; they could be responding to anything from an infection to a wound to too much water Eat or toss? Eat! This only affects the outside of the squash.
The story: Have you ever tried to scrub a squash like this only to find that the “dirt” is attached? In fact, the dry stuff that looks like caked-on dirt is actually more like a permanent scab—something the squash produced to heal up a wound.
In this case the lines on the squash could be healed injuries from some rough collisions with sticks or even grit in the field. The bigger rough spots might represent areas where the squash fought off infection, but still aren’t anything to worry about as it would have been a plant disease (not a human disease) and the issue is probably just on the surface, not deep in the squash.
Too-much water can also lead squash to form bumpy, dirt-like warts. The plant absorbs water faster than it can be used, causing cells to enlarge and burst, and then get sealed over with that wound-healing, dirt-like stuff. Insect nibbles can also lead to the wound-healing that results in a scarred, bumpy squash. For a bunch of great images, check out this page from Michigan State University.