Interwoven, multidisciplinary approaches call on botany, geology, geophysics, geography and other branches of knowledge to bring this elusive prehistory into focus. These studies are teasing out answers by investigating the record of sediment build-up, the profile of ciénaga-drawn cores containing stable sedimentary isotopes, pollen, microscopic charcoal or fire remnants, elemental fractions of organic materials and identifying the sources of the organic matter buried within the sediments. The following time line summarizes several of these studies:21,000 BP — The period of the last glacial maximum when ice sheets throughout the globe were at their maximum extension of the earth, glaciers were at their thickest and the sea levels were at their lowest. The American Deserts were forested, with large pluvial lakes punctuating and rivers flowing across the landscape. The Pleistocene or Ice Age ended, and the Holocene Epoch began.11,500 BP — Stream flows remained strong, capable of moving rocks and cobbles, precluding establishment of most ciénagas, save those few along more protected reaches.8000 BP — Furthest time for which scientists have collected continuous evidence of ciénaga materials to determine when and how ciénagas developed. Water flows remained robust and still prevented the wholesale establishment of ciénagas, a time "when winter precipitation was minimal, fire was rare." "However we do have evidence from the American Deserts of ciénegas deep into the last ice age."7200 BP — Initial stabilization of ciénaga occurred as flows slowed, allowing formation of wetlands. "During most of the past 7,068 years this environment has been slowly aggrading…[although] this generally slow process of accumulating sediments is punctuated by periods of rapid development." 6000 BP — Onset of El Niño/La Niña-Southern Oscillation, warm and cool recurring, alternating, quasi-periodic climate pattern that occurs across the tropical Pacific Ocean and accounts for much of the fire variability in the Southwest.5300 BP — Before this period, woody plants dominated the uplands with "fire episode frequency below (1 fire every 200 years)" and even more infrequent when winter precipitation was low. The transition to grasslands began around this time; after this period, fire frequency increased to "1.3 every 100 years."7200 – 4100 BP — Fine grain sediment increases, suggesting permanent and prolonged annual wetting, stable ciénagas that went through at least three steady states after initial stabilization: · 6300 – 6000 BP· 4700 – 4000 BP· 1600 – 750 BP4500 BP — Due to heavy moisture, a period of river system down-cutting in the Southwest; fire frequency increased to "2.1 fires/100 years" or one fire every 48 years.4100 – 2400 BP — 1,700-year dry interval period where ciénaga water permanence severely lessened, and fire frequency decreased to only "1 fire every 100 years."4100 – 1300 BP — Dominated by grasses, this period was similar to present day.