THE DUMP, a Short Essay:
The dump is/was in fact, a dump. A landfill. Not so much garbage as in banana peels, egg shells and old tin cans (oh, we can't throw those away anymore?) but more in the line of rejected plastics. (What? We can't through those away either?)
The Louis Marx Company, purveyors of plastic toy figures for two+ generations had what can only be described as "very strict" standards for their product. In fact they practiced what today would be called a "zero tolerance" policy. They also did not bother to waste energy by burning or melting down production errors. They simply threw them out. Now production errors ranged from the obvious "mutant" miscasts to very subtle non-standard color variations. There was a specific range of grey, green and brown (and other colors, but those three for Dinosaurs) that encompassed acceptable and anything outside of those parameters got rejected.
Zero-tolerance went beyond what you might expect. If one member of a mold group (the figures were cast in mold groups) was a reject (perhaps the plastic hadn't flowed properly and filled the mold) all the figures would be discarded. This meant that perfectly good figures would be thrown out along with the offending one. For example this dirt encrusted Iguanodon- It looked fine to me, it might have been a color problem, but it was rejected, with prejudice.
Dump Iguanodon encrusted
Rejection took the form of simply being tossed in a barrel, the full barrel thrown on a dump truck, the dump truck would drive out to the factory landfill, and whoosh, slide 'em off to be covered by a grader or a bulldozer. Everyone at the factory and most everybody in the surrounding area knew about the dump but it was privately owned, land owned by the Marx company, and off limits to any and all. Of course environmental restrictions were pretty much non-existent at the time (1950s, 60s early 70s) and did not include the Marx products anyway. It was a cheap and easy way to dispose of what would not be going to market. A very small percentage of total product regardless. The plastic itself did not lend itself to re-melting and re-use and so this form of disposal was as good as any, and better than most. Even better for our purposes today.
After Marx went bankrupt the land became public and someone(s) began exploring the dump site. It was hard work digging out the figures but, at least, when you found one you tended to find a great many in the same immediate area. The trick was to find the sweet spot. Not merely Dinosaurs but modern animals, circus, soldiers, civilians and every other figure made by Marx can be found. If you work hard enough.
As for the Dinosaurs. Prior to 1963 Marx used a 'flat' plastic and the color variation was fairly extensive, varying notably from one lot to the next. In 1963 they switched to what they called the "Heritage Plastic", a waxier, shinier plastic that presumably cast more efficiently and very few of these latter are found in the dump. Prior to 1963 however Marx did a fair amount of experimenting.
One experiment was the creation of "mottled" figures. This involved the mixing of two (or more) colors of raw plastic and creating what was supposed to be a visual representation of the animal in the forest/jungle, a mottled color effect.
Mottled Small Mold Group
Quite often this went wrong. Sometimes the plastics would mix and blend, producing a totally off color, non-standard and unacceptable for retail sale. Other times the mixing resulted in a non-blended result, a spotted creation, two or three toned, and likewise non-standard and unacceptable.
Sometimes the two color plastics didn't really work at all, not mixing properly and cooling at differing rates warping the figure after it was released to cool. This also resulted in an unacceptable level of flash on the figure as it didn't release from the mold quite right- a comparatively common occurrence with the pre-1963 flat plastic anyway.
Dump Struthiomius- miscast: Feet don't sit "flat", legs didn't cool homogeneously. Plus a bit extra "flash" on its head.
So yes- every "dump" figure was individually dug up out of the West Virginia earth. While I personally didn't someone else did.
This Robin's Egg color (for instance) is simply non-standard. You can also see some casting errors in the feet. Some colors just didn't work-out for mass production.
Robin's Egg Sphenacodon
Marx I suspect recognized that if they had just a very few singularity figures on the market, in a color that they could not readily reproduce in quantity (some colors were as a result of Marx engineers experimentation- never meant for the public anyway) they would be creating a skewed market for what they wanted to be selling to the general public. Remember that for the first few years these were sold individually, out of bins in Woolworths and toy stores, only later as carded sets and in the big playsets. They were looking to mass market these, not create a specialty/collectible niche. Yes, many of these are pretty, and unique, but not reproducable for the mass market. ?2011 dinosaur-toys-collectors-guide