Sand spikes are a type of concretion that formed in a very small area on the California/Mexican border.
I can't include pictures but I can give a graphic description. They range in size from about 1 inch to 3 feet. There is a "ball" or cluster of small balls on one end and a tail that tapers off.
Mineralogically, they are calcite based and are completely included with sand. The Barite Roses from Oklahoma do the same thing.
These spikes were first discovered lying loose on the ground from weathering. It wasn't long before people discovered they were in layers below the surface. One well-documented layer was at 3 feet deep and another was at 8 feet.
If that isn't enough to confound people, there is no evidence of fossils of any kind. No trace fossils, no seed fossils, they are just the sand and calcite.
But wait there's more! It wasn't long before everyone involved realized that they all had one other very unique characteristic. In uncovering the beds of them underground they all pointed directly west! The tail of 95% off the ones underground point west--as west as a compass.
Why were they pointing west? No one knows to this day. There have been many theories but so far none can be proven. Some are as funny as aliens. Others think they are some kind of growth that blew over in a windstorm.
When I was growing up every rock shop in the country had a basket of these curiosities. Several dealers went in and used heavy machinery to mine them. Unfortunately they were too soft and most were destroyed. Still many people have one in their collection.
We would love to see them if you have them. E-mail photos to firstname.lastname@example.org, and we'll post them.