FLOOD05245

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Basin: Statewide
• Title: Floods of September, 1970 in Arizona, Utah, Colorado, and New Mexico
• Date: 1/1/1978
• Prepared For: State of Colorado
• Prepared By: USGS
• Floodplain - Doc Type: Flood Documentation Report

2 FLOODS OF SEPT. 1970 IN ARIZ.. UTAH, COLO., AND N. MEX.

. 34'

112"

108'

106"

FLOODS OF SEPTEMBER 1970 IN ARIZONA,
UTAH, COLORADO, AND NEW MEXICO

3.

By R, H. ROESKE, M. E. COOLEY, and B. N. ALDRIDGE

ABSTRA=
During September 5-7, 1970, unusually large floods occurred in the mountains of central
Arizona and in the Four Corners area of Arizona, Utah, Colorado, and New Mexico. Flooding
also occurred in southern and northeastern Arizona. The record-high rainfall of September 5
occurred when a mass of moist tropical air from Pacific storm Norma collided with a cold front
from the northwest. A new 24-hour precipitation record of 11.40 inches (290 millimeters) was
established for Arizona, and new 12- and 24-hour precipitation records of 6.0 inches (152
millimeters) were established for Utah.
The flood took the lives of 23 persons and was reported to have caused about $8.4 million in
damage in Arizona. The main area of flooding was in the mountains in central Arizona. The
flood generally was less destructive with increasing distance downstream; in the Salt and Verde
River basins the reservoirs were capable of storing all the floodwater.
Flooding in the Dolores and San Juan River basins in the Four Corners area was mostly in
rural areas, and two people were drowned in McElmo Creek in Utah. The flood was not as large
as that of October 1911, which is the largest known flood in the area. A second storm occurred in
the Four Corners area September 12-14; however, the amount of flooding generally was less
than that from the previous storm. Flood damage as a result of the two storms was reported to
be about $2.9 million.

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EXPLANATION
_ APPROXIMATE AREA OF FLOOO

INTRODUCTION
During September 5-7, 1970, unusually large floods in the mountains of
central Arizona and in the Four Corners area of Arizona, Utah, Colorado,
and New Mexico (fig. I) transformed the Labor Day weekend into tragedy.
Rapidly rising streams claimed the lives of 23 persons in Arizona and 2 in
Utah. Three other persons died in Arizona as a result of storm-related
accidents; two were killed in a plane crash apparently caused by inclement
weather, and one was killed when a cave entrance collapsed because of
excessive ground moisture. The 23 deaths that were attributed directly to the
flood in central Arizona brought Ihe State's flood dealh toll to 31 for the
summer of 1970; eight persons drowned in flash floods earlier in the summer.
Flooding also occurred in southern Arizona on Seplember 4 and 6 and in
northeastern Arizona on September 5-7; a second flood occurred in the Four
Corners area Seplember 12-14.
More rain fell on September 5, 1970, Ihan on any other day in Arizona's
and Utah's recorded weather history. A new 24-hour precipitation record
was established for Arizona, and new 12- and 24-hour precipitation records

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BASE FROM U.s. GEOl..OGICAL SURVEY
UNITED STATES liMe MAP. 18151

FIGURE 1. -Location of flooded areas.

were established for Utah. Although rain fell over most of Arizona and the
Four Corners area during September 3-6, the large amounts of rain generally
were in the mountains, where the strong orographic uplift exerted great
influence on the amount of precipitation.