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Mystery Cache

World's Largest Roller Dam

A cache by DTCBears Send Message to Owner Message this owner
Hidden : 2/22/2014
In Iowa, United States
2.5 out of 5
2 out of 5

Size: Size: micro (micro)

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Geocache Description:


Lock and Dam # 15 on the Upper Mississippi River is the LARGEST ROLLER DAM IN THE WORLD!

Utilize the information that follows to gather the required pieces of data, then fill in the cache's actual location in the coordinates formula at the bottom.

Without the lock and dam system, river traffic along the upper Mississippi would probably come to a screeching halt.  In its natural state, the Mississippi River is treacherous and wild. There was a time, when rivermen believed that the dangerous and unpredictable Mississippi would never be ‘tamed’.  Since the 1930s, the Corps of Engineers has battled the upper river's natural force with its lock and dam system. Today, the system churns the river, daily upsetting its balance. This "stirring up" has enough calming effect to provide safe river travel.

Contained in a 14-mile stretch of the river just north of Davenport to LeClaire ravaged the dangerous Rock Island Rapids.  In its midst lie submerged rocks, boulders and debris that often caused deadly "snags" adding to the perils of early river navigation. Captains also had to deal with a river bed tangled with limestone chains that reached out into the river from the shoreline.

In 1819 when an Army Corps of Engineers vessel passed beyond the dangerous Des Moines Rapids at Keokuk, steamships began venturing into the Rock Island Rapids. Steamboat traffic carrying tourists and supplies steadily began to increase.

In spite of the captains who braved the river's rough route, the rapids remained dangerous. With increasing settlement and trade, the river's undependable transportation prompted the federal government's involvement in its settlement.  In 1852, Congress passed the Western Improvement Act authorizing $100,000 for early rock-blasting efforts aimed at taming the upper Mississippi.

It was after the Civil War when the Corps renewed its effort to calm the Rock Island Rapids with the beginning of the Corps' Rock Island District. The Corps began to tackle the Rock Island Rapids that lie just upstream from the Government Bridge at the tip of Arsenal Island.

The problem areas of the upper Mississippi were deepened three times, once in the late 1870s, once in 1907. After WWI when traffic of larger vessels increased, the river was deepened to nine feet -- the depth that is maintained today. The Rock Island District Corps oversees 582 miles of 9-foot navigation channel, the second longest channel in the country.

In 1934, with $7.5 million, and about 81 tons of steel, the corps built Lock and Dam 15. Each year, millions of tons of cargo pass through its 8-ton lock chambers on giant barges. (Four million tons would fill 2,666 barges forming a line 50 miles long.)

Lock and Dam 15 was the first of the Corps' 29 lock-and-dam systems.  It is located on the Upper Mississippi River and spans the river between Davenport, Iowa and Rock Island, Illinois.  Construction began in 1931, and the facility was put into operation on March 7, 1934. The dam is 1,203 feet (366.7 m) long, consisting of (11) 109 foot (33.2 m) non-submersible long roller gates, with 11 control houses. Nine roller gates are 19 feet 4 inches in diameter and the two other roller gates are 16 feet 2 inches in diameter.  It is unusual among the upper Mississippi River dams in that it has only roller gates, it has different sizes and types of roller gates, it is not perpendicular to the flow of the river and is one of the few facilities that has a completed auxiliary lock. The main lock is 110 feet (33.5 m) wide by 600 feet (180 m) long and its auxiliary lock is 110 feet (34 m) wide by 360 feet (110 m) long.  Lock and Dam #15 is part of the Upper Mississippi River 9-Foot Navigation Project.  It creates reservoir pool #15 on the Mississippi River.  The river’s waters take an average of 3 hours to travel from pool #14 down to pool #15. The Corps spends $69.5 million a year to keep the system maintained to operate 24 hours a day. Crews conduct day-to-day systems checks to keep it up and running year-round.  

On March 10, 2004, the facility was listed in the National Register of Historic Places as ‘Lock and Dam No. 15 Historic District’ (# 04000175) covering 3,590 acres (1,450 ha), 2 buildings, 9 structures, and 1 object.  The United States Army Corps of Engineers operates Lock and Dam #15.  Walking tours are available for Lock and Dam #15. 

The Lock and Dam also has a river cam that can be viewed at:

Here is the Coordinates Formula for the cache’s actual final location:

North (Y)(A) (H+S)(E+C) . (G+U)(I+Z)(P+N+R),  West (O)(H) (K+bb)(R+T) . (V+B)(D+J)(L+M)

North ___ ___ ___ ___ . ___ ___ ___ West ___ ___ ___ ___ . ___ ___ ___


How many feet long is Lock and Dam #15? = A___ B___ C___ D___

How many control houses are there? = E___ F___

How many feet long is each roller gate? = G___ H___ I___

When was the dam put into operation (MMDDYYYY)? = J___ K___ L___ M___ N___ O___ P___ Q___

How many roller gates are 16 feet 2 inches in diameter? = R___

How many hours does it take the river’s waters to travel from pool #14 down to pool #15? = S___

In what year was Lock and Dam No. 15 listed in the National Register of Historic Places? = T___ U___ V___ W___

What is the National Register of Historic Places number for Lock and Dam #15? = X___ Y___ Z___ aa___ bb___ cc___ dd___ ee___


** Note: Since the formula only requires easy data extractions from the description, and and/or single digit addition, I'm not initially including a geochecker. One can certainly be added later if required.

Congrats on the CO-FTF to drjrm1 and geocacherJoshua

Additional Hints (Decrypt)

Gur pnpur fubhyq or fnsr sebz gur Zvffvffvccv'f fcevat sybbqf.

Decryption Key


(letter above equals below, and vice versa)



61 Logged Visits

Found it 51     Didn't find it 5     Write note 2     Publish Listing 1     Owner Maintenance 2     

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Current Time:
Last Updated: on 9/10/2017 12:15:02 PM Pacific Daylight Time (7:15 PM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum

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