The anastomosed fluvial model, interpreted from modern deposits in the upper Columbia River valley between Radium and Golden, British Columbia, consists of aggrading, multiple, low-gradient, low-sinuosity, thick, sand-filled channels laterally contained by levees, crevasse splays, and various wetland deposits. While active aggrading cross-valley alluvial fans controlled sedimentation in the upper Columbia valley, basin subsidence and/or regional tilting were controls for probable ancient anastomosed fluvial rocks, such as in the Cretaceous Western Interior molasse basin. The uniqueness of anastomosed fluvial style compared to that of meandering rivers is attributed to regional rapid aggradation, which subsequently favors anastomosed deposits for deep burial and preservati n.

In the Columbia valley, the cross-valley profile of anastomosed channel deposits consists of vertically and laterally multiple stringers of channel sand, longitudinally interconnected at different stratigraphic levels. Individual channel cross sections consist of mud-contained, thick channel fills with multistoried textural cycles dominated by planar, tabular cross-bed structures. The upper ¼ to 1/3 of each channel fill consists of either mud or sandy point bar, contained laterally by mud resulting from waning river discharge.

Several different trapping processes may account for hydrocarbon accumulations in ancient anastomosed fluvial sandstones, based on core observations from modern deposits in the Columbia valley. The most common trap occurs in upper channel fill point-bar sands contained laterally and above by mud. A less common trap is a sand-filled channel segment plugged at both ends with a mud-filled master channel and capped with lacustrine mud. Two other traps result from differential compaction of mud versus sand: (1) deep scour holes at the downstream confluence of two channels allow the thicker sand-filled scour to form a domelike "compaction high" when capped with mud; and (2) a cross overlap of two stratigraphically different channels results in an anticline of the upper channel where it cros es over the lower channel.

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