Essentially, what you are looking at is a pit with two beaker bowls and a bunch of pulverized beakers on top. Sometimes a gold artifact, an amber bead or bunch of arrowheads are deposited, then covered with stones.
To add to the weirdness, only occasionally is a single body part located within similar pits. So re-approaching the situation, it seems in some of these cases we might be able to point to a few possible facts:
The ceremony was attended by multiple individuals who drank and then smashed their beakers. In the Ambrona Valley, it seems two bowls are set inside the pit. One or two individuals deposited something of value to them. The pit is enclosed and preserved as a monument to this event.
In this light, several scenarios might be cause for a meeting such as this. I'm shooting from the hip as always:
1) Tribal arbitration? Literally, to "bury the hatchet", make peace, end a dispute, bury the past.
I'm sure these people had boundary disputes, failed marriages, in-law wars, cattle theft, broken contracts, etc.
2) Covenants? These people sold land, bonded brides, made deals, and contracted wainwrights. When you make a covenant, you will make a bloody oath and drink to it. When you proclaim your oath, cut your hand and raise your glass, a bunch of drunk guys with daggers are going to remember what you said that night.
3) Harvest ritual? There might be a lot of organic stuff that didn't survive, like "corn mothers", effigies or dolls. Stalks may have been piled at the end of the harvest and covered with stones. So the materials could literally be offerings.
BEAKER BARROWS (not) for the dead: El Alto I & III, Las Cuevas/El Morrón and La Perica (Soria, Spain) CuPAUAM 40 Manuel A. Rojo-Guerra1, Rafael Garrido-Pena, Íñigo García-Martínez-de-Lagrán, and Cristina Tejedor-Rodríguez, 2014 [Link]
In this article we will discuss on a peculiar and interesting feature recently discovered in the archaeological record of Copper Age Bell Beakers in the Ambrona Valley (Soria, Spain), that is the existence of barrows which look like tombs but they were not. They even include valuable items (finely decorated pottery, gold jewellery) but no sign of human bones. This absence could not be explained by selective preservation of the materials, since those barrows are not located in acid soils, and faunal remains are usually found in other sites of the same area. We could interpret this special finds as the archaeological testimonies of eventual ceremonial activities, perhaps including commensality rituals (intentionally broken pots are found inside them), being the stone mound the commemoration in the landscape of those important events (a possible cenotaph evoking the death of someone important away from his hometown?) or places (the location of special features of the environment in their mythic geographies).