Little Spokane River EarthCache
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The Little Spokane River is a tributary of the Spokane River and is approximately 35 miles long. It drains the rural area of forested foothills and a farming valley north of the city of Spokane along the Idaho-Washington border.
The Little Spokane River rises in southern Pend Oreille County, south of Newport near the Idaho state line. It then flows south/southwest past Milan and Colbert, Washington. It joins with the Spokane River from the east, approximately 10 miles northwest of the City of Spokane.
North of the City of Spokane groundwater in the Spokane Valley / Rathdrum Prairie Aquifer flows in a northward direction toward the Little Spokane River, following the ancestral channel of the Spokane River. Unconsolidated sediments have filled this channel (referred to as the Hillyard Trough) to a depth of over 700 feet. Several large capacity springs are dispersed over an approximate two mile wide area along the interface between the Hillyard Trough and the Little Spokane River Valley. This area has been recognized as a primary regional discharge zone for the Spokane Valley ' Rathdrum Prairie Aquifer. The springs typically discharge 30 to 100 feet above the Little Spokane River, and are fed by groundwater from the Spokane Valley / Rathdrum Prairie Aquifer. Stream flow in the Little Spokane River increases approximately 250 cfs (Cubic feet per second) over this reach of the river, in response to the groundwater discharge.
The Spokane Valley / Rathdrum Prairie Aquifer within the Hillyard Trough historically has been described as a single, largely unconfined unit, developed within unconsolidated Quaternary flood deposits. Hydrogeologic investigations and literature review conducted in support of two Spokane area wellhead protection projects have provided evidence of a deep, areally extensive, confined aquifer that extends from the north Hillyard Trough into the lower reaches of the Little Spokane River Valley. This secondary, deeper aquifer is present within the north Hillyard Trough at depths of 300 to 500 feet below ground, and is overlain by 150 to 200 feet of low permeability sediments. These low permeability sediments are typically encountered between elevation 1450 and 1650 FAMSL beneath both the Hillyard Trough and Little Spokane River Valley, and may represent remnants of a glaciolacustrine (lakebed) deposit. Within the Little Spokane River Valley, the deep confined aquifer system is encountered at depths of approximately 100 to 150 feet below the valley floor.
This earthcache will bring you to the Little Spokane River where it flows through the Haynes Estate Conservation Area, which is maintained by the Spokane County Parks and Recreation Department.
You can reach the Haynes Estate Conservation Area from the east or the west. Coordinates for both entry locations are posted.
To receive credit for this Earthcache, you must complete the following 3 requirements.
1) Upload a picture of yourself at the posted coordinates with the Little Spokane River as your background. Please also describe any wild life you saw while visiting this earthcache.
2) Determine the flow rate in "Feet Per Second" for the Little Spokane River. This may be done by measuring & marking a distance along the different river bank, then tossing in a leaf upriver from your starting point. With a stop watch, time how long it takes your leaf to complete your measured distance course. Then calculate that into "Feet Per Second" for the river.
3) Estimate how deep the river is at the bend and how wide it is at the bend.
Your picture must be posted with your log entry and your answers E-MAILED to Martin 5.
Congratulations to Trev of The Steaks for being first to complete the logging requirement on this EarthCache on the same day it was published!!
Martin 5
Platinum Level EarthCache Masters
For more information about the aquifer see the following earthcache: The Rathdrum Prairie - Spokane Aquifer, by Three Bottles (GC1AA9M).
For more information about the Spokane River see the following earthcache: Fort Sherman, by Martin 5 (GC1HGAW).
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