Is this something that just appeared out of nowhere rather than being planted planted by somebody?

It appeared in the old hog pen, along with several others
like it that I removed. I allowed it to grow on the fence just to see what it would become! (I also got two cucumber vines that way and they are producing delicious,small fruit!) This monster, however, I can't figure out! It almost resembles a giant roundish zucchini, in color, but lighter.

Perhaps it is a gourd.

It is more than likely a gourd as esh says. That beautiful coloration won't last as that is just the skin which will dry up and become moldy. The underneath shell of the gourd will be a beige eggshell color. The weight will change too as it matures and transpires through the vine it is attached to. Allow it to dry on the vine. It should be ripe when it becomes light and the seeds rattle inside. They make good birdhouses. If it is not a gourd then my second guess is that it is something in the squash family, probably some mutated inedible hybrid.

I would have thought. by it's size, it's a gourd. but it doesn't have that "pear" shape. It is more round, like a melon of some sort, but when I plucked some female flowers
off, the base lump smelled like yellow squash.
With my luck, it's probably a mutant hybrid, inedible as you suggest, Eddie!

Maybe it's one of those Squmpkins that were mentioned in an earlier thread. It actually sounds like a watermelon or gourd though.

Squmpkins? I'll check it out--Thanks!

I suspect it's a citron. (that's from the farm-boy DH) That's a melon that's sort of a hard fleshed watermelon. In some areas it's considered wild. The rind can be preserved and used in fruit cakes, etc. It may have been planted around the pen to provide quick shade.

i think citron, as well. they are weeds in the southern portions of my state and can be seen around cultivated field borders and roadbanks.

Here is a link that might be useful: citron vine

Good link, Jeff. I noticed that it says:

"Citron is often referred to as stock melon and preserving melon. It should not be confused with the citron of the citrus fruit family (Citrus medica) whose peel is candied and frequently used in fruitcakes. "

The "fruit" has been removed from the vine. I took photos which I will try to put up soon. The stem began to turn slightly yellow, so I cut it off. It really looks like an oversized, round zucchini...It has five prominent ribs that are dark green, and the leaves of the vine are shaped like squash, not cucumber or melon. I can hardly wait to cut it open, just to see inside!!

as of today, the "squmpkin" has begun to turn orange on the blossom end and around the stem base. Should I let it "ripen" to total orange, or cut it open? Suggestions, anyone? (Sorry I haven't got the photos yet---it's my son's computer camera, and I don't know how to transfer them! Have to wait until he has time!)