Ricks Spring EarthCache

Ricks Spring Cavern has been a traditional wayside stop for generations. Early settlers filled up jugs of spring water, until they realized the water was causing stomach and intestinal discomfort. It was later discovered that what was thought to be a natural spring was actually an underground diversion of the Logan River.

Ricks Spring

Karst features in the Logan Canyon area are indicative of a hydrologic system that is developed within more than 3,000 ft of Paleozoic limestone and dolomite. Karst features in this alpine region include large springs that discharge along major rivers, losing streams in tributary drainages, caves and pits, blind valleys, sinkholes, dolomite pavement, and surficial karst (karren). Glaciation occurred above 8,000 ft during the Pleistocene, resulting in destruction of karst landforms that developed during interglacial periods (Wilson, 1976). Speleothem age-dating, fluvioglacial deposits in caves, and deranged topography indicate that existing karst features, particularly caves, are largely remnants of former karst landscapes.

Karst systems in alpine terrains are substantially different from those in relatively flat-lying strata in more temperate regions. Characteristics of alpine karst systems include a large component of vertical solution development and a thick unsaturated (vadose) zone, steep hydraulic gradients, spring discharge that responds primarily to snowmelt runoff, pit development in high-altitude meadows, and cold-temperature dissolution of carbonate rocks. To better characterize the hydrologic system in this alpine karst, an investigation was begun to (1) determine variations in discharge of selected large springs; (2) correlate temperature and specific conductance of spring water with changes in discharge; (3) determine recharge areas for the springs and general directions of ground-water flow; (4) delineate ground-water basin divides; (5) determine ground-water travel times; and (6) evaluate the effects of geology on ground-water movement.

HYDROGEOLOGY

The Bear River Range consists in large part, of a thick sequence of carbonate (limestone and dolomite) rocks that range in age from Cambrian to Mississippian (Dover, 1987). The principal geologic units in this area and approximate thicknesses are the Garden City Formation (1,400 to 2,000 ft), Swan Peak Quartzite (200 to 400 ft), and Fish Haven Dolomite (350 ft) of Ordovician age; the Laketown Dolomite (1,500 to 2,000 ft) of Silurian age; the Water Canyon Formation (425 to 600 ft), Hyrum Dolomite (850 ft), and Beirdneau Formation (1,000 ft) of Devonian age; and the Lodgepole Limestone (750 ft) of Mississippian age. Karst is more developed in the Garden City Formation and Laketown Dolomite than in the other carbonate units. All of the units, however, are capable of transmitting water along dissolution-enhanced fractures, faults, and bedding planes. The Swan Peak Quartzite is probably a barrier to downward movement of water from the Fish Haven Dolomite to the Garden City Formation in some areas and likely influences the direction of ground-water movement. All of the formations make up the upper part of a large regional structure, the Logan Peak syncline (Williams, 1948) . The syncline plunges to the southwest at about 15 degrees and rocks on the west limb dip at a considerably steeper angle than those on the east limb. This structural feature and associated fractures influence the movement of ground water in much of the region.

Aquifer Recharge

Recharge to the carbonate aquifer takes place through point sources (sinkholes and pits), as seepage losses through fluvioglacial deposits that fill valley drainages, and as infiltration along ridges and valley slopes. Sinkholes (dolines) and pits are typically developed in high-altitude meadows where snow accumulates and may persist throughout much of the year. Water entering point sources moves vertically downward along solution-enlarged fractures to principal conduits that channel water to the springs. Pits range in depth from less than 100 to as much as 300 ft, but many of these have been occluded by fluvioglacial materials consisting primarily of quartzite boulders. Fluvioglacial deposits also form a veneer over carbonate bedrock in valley drainages. These deposits are very permeable and streams typically sink into the streambed along distances of several hundred yards rather than in distinct point sources such as swallow holes. These losing reaches are probably related to fracture zones within the underlying bedrock. Most streams in these alpine drainages are fed by snowmelt runoff and, therefore, tend to be seasonal. During periods of peak runoff, however, streamflow that is not lost to the underlying bedrock continues down surface- water courses to the Logan River. Infiltration of snowmelt along ridges and valley slopes provides an additional component of recharge to the aquifer and probably moves along diffuse pathways through the fractured-rock matrix. Diffuse flow can be a significant component of long-term storage in the aquifer and maintenance of base flow of springs.

Discharge from Springs

Discharge from the carbonate aquifer is primarily from large springs along the Logan River. The Logan River is the principal base level stream for ground- water discharge in this part of the Bear River Range. Three second magnitude (average discharge between 10 and 100 cubic feet per second (ft³/s)) and two third magnitude (average discharge between 1 and 10 ft³/s) springs, along with several smaller springs, discharge along the north and west sides of the river . These include Dewitt, Wood Camp Hollow, Logan Cave, and Ricks Springs. Only one large (second magnitude) spring is known to discharge along the south side of the river . Collective discharge of the springs provides a substantial component of streamflow in the Logan River. Wilson (1976) estimated that the combined flow of Wood Camp Hollow, Logan Cave, and Ricks Springs could be as much as 20 percent of the discharge of the Logan River. Spring discharge responds primarily to snowmelt runoff, with peak flow from late spring to early summer and base flow during the winter months .

Figure 2. Hydrograph showing typical seasonal response of an alpine karst spring to snowmelt runoff, Dewitt Spring, Logan Canyon, Utah, January 1995 to January 1998 (Data from City of Logan Water Department, written commun., 1998).