in Vargas State. Many of these people lived atop alluvial fans formed by debris flows sourced out of the peaks to their south. Rainfall December 1999 was unusually wet along the north-central Venezuelan coast. The first, and less powerful, storm that month occurred 2–3 December and dropped of rain on the coast. Two weeks later, in a 52-hour span during 14, 15 and 16 December 1999, of rain (approximately one year's average total rainfall for the region) was measured on the north-central coast of Venezuela at Simón Bolívar International Airport in Maiquetia, Venezuela. These heavy rains included of accumulation in just one hour, between 6 and 7 AM on the 16th; precipitation on both the 15th and 16th exceeded the 1,000-year probability rainfall event. Even so, the coast received much less rain than some regions upstream. This sudden and intense storm was especially unusual because it occurred in December, while the typical rainy season in coastal Venezuela lasts from May to October. These out-of-season rains formed when a cold front interacted with a moist southwesterly flow in the Pacific Ocean. This interaction produced moderate to heavy rainfall starting in the first week of December and culminating in the 14–16 December event that caused the deadly floods and debris flows. The heaviest rains were centered around the mid-upper part of the San Julián basin, which feeds water and sediment onto the Caraballeda fan. Heavy rains persisted within of the coast, and subsided on the Caracas side of the Cerro El Ávila. Rainfall rates also decreased westward toward Maiquetía. Geology Bedrock The bedrock in the region surrounding Caracas is mainly metamorphic. From the coast and extending approximately inland, deeply foliated schist of the Mesozoic Tacagua Formation is exposed. Soils forming on them are fine-grained (clayey), thin (), and often colluvial. Although the A horizon of the soil is often less than thick, the bedrock is often weathered down to greater than . Further inland, gneisses of the Paleozoic San Julián Formation and Precambrian Peña de Mora Formation extend to the crest of the Sierra de Avila. These units have thin soils over less-weathered bedrock; this is believed to be because of rapid erosion due to the steep slopes in this area. Because foliation planes are planes of weakness, these fabrics within the rocks strongly influence landslide and debris flow hazards. Where the foliation planes are dipping towards a free surface, failure is