Well defined cyclic deposits are recognized in late Cretaceous deposits of the Rocky Mountain region. Excellent exposures in east-central Utah exhibit the following sequence of units from the base upward: (1) marine shale, (2) littoral marine sandstone, (3) lagoonal deposits, and (4) coal. These units were in large part deposited simultaneously during a period of slow eastward regression of the Mancos sea; hence, a complete sequence is rare. The slow regression was punctuated by numerous sharp pulses of basinal subsidence which produced rapid, westward transgressions of varying magnitudes. The result was numerous repetitions of four nearly simultaneously existing environments whose deposits constitute a fairly standard sequence of units (the basic cyclothem.)

The occurrence of petroleum in lagoonal deposits suggests derivation in situ but may be due to better opportunity for preservation in lagoonal areas.

Criteria are presented for recognition of cyclic deposits and their individual components, both in outcrop and in the subsurface. Because of rapid intertonguing and variations along the shore line, long-range correlations are usually unreliable; but if one has a full knowledge of the nature of the intertonguing, correlations over short distances can be detailed and reliable.