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OBJECTIVES: The scale of sequence recognition shifts to major first-order sequences, which may be called Sloss sequences or megasequences. The Kaskaskia-Absaroka sequence boundary is seen at STOP ONE and the Zuni-Tejas sequence boundary is seen at STOP THREE. A higher order sequence boundary within the Absaroka sequence that has been enhanced by local tectonic activity producing an angular unconformity is seen at STOP TWO. An objective today is to emphasize the effects of recurrent movement of basement faults on stratigraphy and sequence boundaries. These effects may be seen on outcrop in the San Juan Mountains, but their effects continue in a more subtle manner in the subsurface of the San Juan Basin, the site of the next two days of stops.

Leaving Grand Junction, drive south to US 50 east. The road log begins at the junction of US 50 and CO 146 approximately eight miles southeast of Grand Junction.

0.0 Junction of US 50 and CO 146 near Whitewater. View of Book Cliffs to north and west, Uncompahgre uplift to west, and Grand Mesa (approximately 10,000 feet in elevation) to east, capped by Pliocene (9 Ma) lava flows. The road between here and Delta is in the lower Mancos Shale. The underlying Dakota Sandstone and Burro Canyon Formation may be seen to the west in the Gunnison River valley and close along the road in places. The rest of the Mancos Shale forms the hills to the east

31.0 Delta. Confluence of Gunnison and Uncompahgre rivers. Continue on US

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