After the mesquite pods had been processed, sometimes there was a fall bonus if acorns came into season. For millennia, the most common oak tree in Erath County has been the post oak (Quercus stellata), which prefers to grow outside the Bosque Valley in sandy soil. The liveoak (Quercus virginiana) grew in the dark soil formed by dissolving limestone and grasses on the prairies and floodplains. The largest oak with the largest acorn, is the burr oak (Quercus macrocarpa) whose range spread from the Bosque Valley during times of increased moisture. The acorn crop depended on the masting cycle. Typically, oak trees would bear a heavy crop (mast) once in every three to five years. The strategy is intended to satiate predatory insects and rodents, allowing some acorns to sprout. Then starve them for a few years to keep their numbers low. The masting cycle responds to a collective signal not yet understood. The current theory is that the average temperature and rainfall in the spring can trigger oaks across several counties, to bloom at the same time. The time that the bloom occurs in the spring may decide what per cent will pollinate and become acorns. A careful observer, like a Native shaman, might have been able to make predictions accurate enough to plan for an acorn crop. Pollen studies show that during droughty years, rare acorn crops would have been a cause for celebration. In those years the acorns would have been boiled to get rid of the toxins, so that the pulp could be ground on metates, dried, and stored for winter as flour.