A SNOW HYDROLOGY STUDY OF THE
HORSE MOUNTAIN SKI AREA IN HUMBOLDT COUNTY
by
Ross A. Carkeet, Jr.
A Thesis
Presented to
The Faculty of Humboldt State College
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
June, 1968 Approved by the Master's Thesis Committee
Chairman
Approved for the Graduate Study Committee ABSTRACT
A snow hydrology study was conducted during the
winter of 1966-1967 to determine snow cover character- istics and snow water storage in the higher elevations of the Coast Ranges within Humboldt County, and also to
provide insights on the winter recreation potential of the Horse Mountain Ski Area. Winter climatic and snowfall data were collected from a weather station on Horse
Mountain and from available historical sources. Snow cover characteristics were sampled in two drainage basins on Horse Mountain using the Mount Rose snow sampler and other instruments, including a calorimeter to determine snow quality.
The results obtained from historical climatic information strongly suggest that snow cover was adequate to permit at least two months of skiing during all but five seasons in the last 22 years on Horse Mountain.
During the study period, an average snow depth of 30 inches and water equivalent of 13 inches, with an average snow quality of 93 percent, provided suitable snow conditions for skiing during 56 percent of the time from iv
December through May. A total of 2,380 skier days were recorded on the site during the study period.
Elevation, exposure and slope steepness played a major role in affecting snowfall accumulation and reten tion on north slopes of Horse Mountain. Random sampling from points located on the ground with aerial photographs provided an acceptable method of determining average snow depth and water equivalent within study basins throughout the winter. From the variability found in this study, a sample size of 24 points would provide an estimate of snow depth and water equivalent in basins within 10 percent at a confidence level of 90 percent. A linear regression analysis relating temperature to solar radi- ation in this area of Humboldt County yielded a correlation coefficient of 0.93.
It appears that snowfall is more important to the hydrology of higher elevations in Humboldt County than has been noted previously. There had formerly been almost no factual snow hydrology data for higher elevations in this region. To illustrate the significance of snowfall,
April snow water storage on slopes during the study period was 19.2 inches, or 27 percent of the total annual precipitation of 70 inches. ACKNOWLEDGMENTS
This study was financed by matching federal funds from a McIntire-Stennis Cooperative Forestry Research
Grant. The author is most grateful for this support.
Appreciation is also extended to graduate students
Gerald A. Ahlstrom and Michael F. Taylor for their competent field assistance, as well as to Taylor D.
Robertson of the United States Forest Service, and to
Dr. Jack Walsh and Weldon A. Benzinger of the Humboldt
Ski Club for their generous cooperation which materially contributed to this study.
Sincere gratitude is also extended to Mr. Douglas
J. Jager, formerly of Humboldt State College, for his instrumental role in initiating this study. The author further expresses a warm thanks to Dr. Forrest D.
Freeland, Jr., thesis committee chairman, for his unceasing encouragement and guidance, and to the other members of the graduate committee for their assistance.
Finally, the author expresses lasting gratitude to his wife, Sharon, for her encouragement and patience relative to this endeavor. TABLE OF CONTENTS
Page
ABSTRACT iii
ACKNOWLEDGMENTS
LIST OF TABLES viii
LIST OF FIGURES xi
INTRODUCTION 1
Objectives and approach 1 Project justification 2 Literature review 3
THE STUDY AREA 8
Location and access 8 Ownership and management 10 Physiographic description 10 Climate 10 Geology 11 Drainage and topography 13 Aspect 14 Soil and vegetation 15 Aesthetic qualities 16 Winter recreation facilities 16 History of area 17 Methods 17 Winter recreation use 17 Intensity of recreation use 22 Climatic history 25
STUDY METHODS 31
Definition of study basins 31 The weather station 36 Location and establishment 36 vii
Page
Instrumentation 36 Snow quality 39 Snow sampling points 42 Sample size 42 Method of selection 43 Method of establishment 44 Measurement 46
DISCUSSION OF RESULTS 48
Analysis of individual storms 48 Description of 1966-1967 winter 49 Weather station analysis 56 Humidity 56 Temperature 58 Snow density 60 Precipitation 63 Solar radiation 68 Correlation of solar radiation to snowmelt 71 Snow quality analysis 75 Results 75 Double distance thermographs 77 Analysis of snow sampling results 78 Variation between study basins 78 Variation within basin 82 Theoretical sample size determination 84 Snowfall accumulation and retention in basins as related to physiographic parameters 88 Elevation 88 Exposure 91 Aspect 92 Slope steepness 94 Crown canopy 95 Recreation use during 1966-1967 winter 97 Observations during field work 100 Problems encountered during field work 101
CONCLUSIONS 103
LITERATURE CITED 107
APPENDIX 111
LIST OF TABLES--TEXT
Table Page
1. Numbers of skiers and snowplayers who visited the Horse Mountain Ski Area from 1962 to 1967 23
2. Number of participants in all winter recreation activities from 1947 to 1966 in the Lower Trinity Ranger District of Six Rivers National Forest 24
3. Evaluation of skiing potential on Horse Mountain from 1946 to 1967 during months of February to May 27
4. Relative humidity measurements on Horse Mountain during the winter of 1966-1967 ... 57
5. Periodic density measurements of freshly- fallen snow on Horse Mountain during the winter of 1966-1967 62
6. Theoretical solar radiation snowmelt on Horse Mountain as compared with observed snowmelt from all heat sources 73
7. Comparison of snow depth and water content between the developed and undeveloped study basins using Student's "t" test 81
8. Comparison of snow depth and water content between ski slopes and forest adjacent to the slopes in the developed basin using Student's "t" test 83
LIST OF TABLES--APPENDIX
Table Page
9. Physiographic parameters measured at each snow sampling point in the study area 112
10. Scientific and common names of all conifers and common shrubs found in the Horse Mountain Ski Area 115
11. Depth and water content of snow at Big Flat in Trinity County (elevation 5,100 feet) from 1946 to 1967 116
12. Known and estimated snow depths for the Horse Mountain general area from 1946 to 1967 117
13. Horse Mountain snow survey data sheet 118
14. Monthly rainfall and snowfall on Horse Mountain during the winter of 1966-1967 119
15. Analysis of individual storms on Horse Mountain during the winter of 1966-1967 120
16. Weekly snow measurements from the Horse Mountain weather station during the winter of 1966-1967 122
17. Seasonal precipitation and temperature data from Salyer and Honor Camp 42 during recorded years of measurement 123
18. Depth and water content of snow on Anthony Peak in Tehama County (elevation 6,200 feet) from 1946 to 1967 124
Table Page
19. Monthly temperature measurements on Horse Mountain during the winter of 1966-1967 125
20. Temperature and solar radiation data used in regression relating weekly solar radiation to mean daily temperature for weekly period 126
21. Snow quality measurements on Horse Mountain from January to May 1967 127
22. Description of formulas used in computing t values 128
23. Average snow measurements in the study basins on Horse Mountain from January to May 1967 129
24. Average snow measurements on ski slopes and in the forest adjacent to slopes on Horse Mountain from January to May 1967 130
25. Average snow measurements from each sampling point on Horse Mountain from February 18th to May 21st 1967 131
26. Recreation use on Horse Mountain during the winter of 1966-1967 133
LIST OF FIGURES
Figure Page
1. Map of California Snow Zone 5
2. Mean annual snowfall in Humboldt and Del Norte Counties 7
3. Location map of the Horse Mountain Ski Area in Humboldt County, California 9
4. General area map of Horse Mountain, illustrating access, bordering ownership, drainage, and location of historical skiing areas 20
5. Topographic map of the Horse Mountain Ski Area, showing the study basins, snow sampling points, and other detail features extracted from August, 1966 aerial photographs of 1/12,000 scale 32
6. Developed basin as seen from the northeast on February 4, 1967 from snow sampling point number three (elevation 4,350 feet) 34
7. Humboldt Ski Club lodge located below intermediate slope in the developed basin 34
8. Undeveloped basin as seen from the northeast on April 2, 1967 from snow sampling point number 43 (elevation 4,400 feet) 35
9. Undeveloped basin near snow sampling point number 44 (elevation 4,440 feet) 35
xii
Figure Page
10. Weather station as seen from the southwest, illustrating recording rain gage and fabricated alter shield, with pyrheliograph attached in rear 40
11. Weather station as seen from the northeast on April 30, 1967 when snow depth attained a seasonal maximum of 87 inches 40
12. General weather pattern in the western United States on March 13, 1967 54
13. Comparison of mean monthly temperature on Horse Mountain (1966-1967) with mean monthly temperature from Honor Camp 42 from 1961 to 1967 59
14. Comparison of monthly precipitation on Horse Mountain (1966-1967) with monthly precipitation in Salyer from 1949 to 1967 64
15. Snow depth fluctuation at the Horse Mountain weather station during the winter of 1966-1967 with comparative depths during months of data availability from the nearest permanent snow survey courses 67
16. Snow depth marker located immediately south of the weather station indicating a snow depth of one inch on November 20, 1966 69
17. Snow depth of 76 inches on April 22, 1967 69
18. Relationship of mean daily temperature per weekly period to weekly solar radi- ation during the period from February 11th to June 2nd on Horse Mountain 70
xiii
Figure Page
19. Snow quality fluctuation on Horse Mountain during January through May 1967 76
20. Snow depth and water content fluctuation in both study basins on Horse Mountain during January through May 1967 80
21. Mean snow depth in developed and undeveloped basins from February 18th to May 21st 1967 89
22. Relationship of skiing potential on Horse Mountain to actual use during the winter of 1966-1967 99 INTRODUCTION
Objectives and approach
The primary intention of this study was to procure basic information concerning snowfall, snowmelt, and other winter climatic characteristics little known for the higher mountain areas in Humboldt County. A secondary intention was to evaluate the winter recre- ation potential of the Horse Mountain Ski Area as an example of the possible winter sports resources available in Humboldt County.
The objectives of the study were accomplished by means of the following specific methods: (1) establish- ment and periodic measurement of semi-permanent snow sampling networks within two drainage basins on Horse
Mountain having different physical and land-use characteristics, (2) establishment and maintenance of a weather station for acquiring climatic data to determine the quantity and quality of the snow in the immediate vicinity of the ski area, (3) compilation of existing information concerning climatic and winter recreation 2 history of the Horse Mountain Ski Area and adjacent areas, as well as the measurement of present winter recreation use, and (4) an incorporation of results from the above to determine the feasibility for further development of winter recreation facilities in the ski area.
Project justification
The absence of quantitative snow data for the upper regions of Humboldt County was in itself adequate justification for support of this study. In the literature, opinions of various authors are inconclusive as to the significance of the contribution of snowmelt from the higher regions of Humboldt County to peak flows of northern California rivers during the 1955 and
1964 floods (Southern Pacific Railroad Company, 1965,
United States Army Corps of Engineers, 1965, and Zinke,
1965). Authors provide no local snow pack data to support hypotheses, and in this respect their opinions are unsubstantiated. The need for quantitative snow information under these circumstances was obvious. 3
A portion of the California Public Outdoor Recre- ation Plan attesting the present and future importance of marginal winter sports areas in California was another important justification for this study. The 1960 report emphasizes the importance of marginal ski areas in serving beginning skiers and for serving those who can neither afford nor find time to patronize the higher elevation and more distant ski resorts (California
Public Outdoor Recreation Plan Committee, 1960).
Literature review
In 1947, Wesley Hotelling, District Ranger of the
Lower Trinity Ranger District of Six Rivers National
Forest, conducted a snow survey of the Titlow Hill area near Horse Mountain (Figure 4, page 20) to determine the potential of the area for development of winter skiing.
Preliminary surveys on January 17th and 18th indicated a snow depth of 14 inches on Titlow Hill (The Humboldt
Times, January 30, 1947). At this time the area was acclaimed by William Fischer, Supervisor of Six Rivers
National Forest, as representing the best site for snow sports development in northwestern California. Access to 4 the area was realized as a major problem in meeting the demand for winter sports in northern California.
The California Snow Zone consists of a boundary established by the Forest Service to include only those areas in California where measurable snow persists on the ground during the entire winter period (Anderson, 1963).
As Figure 1 indicates, Humboldt County is excluded from the snow zone boundary. East of Eureka the zone extends west to include the Salmon-Trinity Alps Wilderness Area.
Southeast of Eureka the snow zone encompasses the Yolla
Bolly-Middle Eel Wilderness Area. Lower limits of the zone extend to 3,500 feet elevation in extreme northern
California and to 5,000 feet in the southern Sierra
Nevada northeast of Bakersfield. Dr, James L. Smith, project leader for the Forest Service Central Sierra Snow
Laboratory, informed the author that many areas in north- western California that are presently excluded from the snow zone might be eligible for inclusion if more local meteorological and hydrological information were available.
A map illustrating average seasonal snowfall in
Humboldt and Del Norte Counties was devised by the United 5
DRAWN FROM A MAP OF THE CALIFORNIA SNOW ZONE BY ANDERSON (1963); PACIFIC S.W. FOR. & RNG. EXP. STA. BERKELEY, CALIFORNIA.
Figure 1. Map of California Snow Zone. 6
States Weather Bureau in 1964 (Figure 2). The reliability of the map is subject to question however, since iso-lines of average seasonal snowfall are constructed using an unrecorded length of measurement period and limited ground control. In addition, only sparse low elevation snow measurements are offered as a quantitative basis for map construction. Furthermore, the map grossly under- estimates high elevation snowfall as based upon findings recorded during the winter of 1966-1967. In discussing the climate of Humboldt County, the Weather Bureau implies the limited applicability of the above map at higher elevations and emphasizes the general unavail- ability of major snowfall data by stating:
Snowfall is infrequent at all points along the coast and in the lower portions of the river valleys, and seasonal totals are generally less than an inch or two. In the mountains there is snowfall every winter, and seasonal totals at many points exceed 35 or 40 inches. Records are not available to show the snowfall accumulation near the crest of the mountains, but it seems likely that depths of 150 inches would be found in some areas (United States Weather Bureau, 1964).
Extensive research in snow hydrology has been carried on by the Forest Service in far distant areas such as the Central Sierra Snow Laboratory, and at Fraser
Experimental Forest, Colorado. 7
DRAWN FROM A MAP DEPICTING MEAN ANNUAL SNOWFALL IN HUMBOLDT & DEL NORTE COUNTIES AS PREPARED BY THE U. S. WEATHER BUREAU, SAN FRANCISCO, CALIF. 1964.
Figure 2. Mean annual snowfall in Humboldt and Del Norte Counties. THE STUDY AREA
Location and access
The Horse Mountain Ski Area is located 35 miles east of Eureka near the mideastern boundary of Humboldt
County. Primary access to the area is provided east from
Arcata via State Highway 299 to Berry Summit (Figure 3).
From Berry Summit, five miles of improved dirt road leads southeastward to the ski area. The responsibility for snow removal on this road is vested with the Humboldt
County Road Department. Since 1954, winter maintenance of the road leading to Horse Mountain has been necessi- tated by the presence of a radio communications system complex on the summit which serves numerous public agencies throughout Humboldt County. Potential access to the ski area is provided westward from Salyer on the
Friday Ridge and Titlow Hill roads (Figure 4, page 20).
However, these roads are inaccessible in winter due to blockage by snow.
Horse Mountain is the closest winter sports area to the Humboldt Bay Region of northern California. The 9
Figure 3. Location map of the Horse Mountain Ski Area in Humboldt County, California. 10 ski slopes are within a 90 minute ride from Eureka, whereas the next closest ski areas are located at Mount
Shasta, California, and Ashland, Oregon. Both sites require five hours travel time by automobile from Eureka.
Ownership and management
The ski area is established immediately within the western boundary of Six Rivers National Forest, under jurisdiction of the Lower Trinity Ranger District.
Private land bordering on the west is awned by Simpson
Timber Company as illustrated in Figure 4 (page 20).
Management of the ski area is by the Humboldt Ski
Club under the financial administration of Dr. Jack Walsh of Eureka. The site is leased from the Forest Service on a commercial recreation use basis.
Physiographic description
Climate
In contrast to the moderate climate of the Pacific coastal belt, the study area is located far enough inland from the coast for the climate to be continental in char- acter, with large variations existing between diurnal and 11 annual temperatures. Consequently, the renowned
Austrian climatologist Dr. Wladimir Köppen has classified the interior climate of higher elevation northwestern
California as humid-microthermal, characterized by cold, wet winters and warm, dry summers. More specifically, the climate is classified by the Köppen system as "Dsb."
The limits of each letter of classification, which are based upon annual and monthly means of temperature and precipitation are described as follows (Trewartha, 1954):
D: microthermal, cold-snowy forest climate; average temperature of coldest month below 26.6 degrees F., average temperature of warmest month above 50 degrees F.
s: summer dry; at least three times as much rain in the wettest month of winter as in the driest month of summer, and the driest month of summer receives less than 1.2 inches.
b: average temperature of warmest month during summer under 71.6 degrees F.
Geology
Horse Mountain is located within the Klamath
Mountains geomorphic province, an area characterized by accordant summit levels and highly dissected old land surfaces. Ultramafic, serpentinized rocks of the Mesozoic age are an abundant component of the subjacent terrain in 12 this province, and a vast outcropping of the same virtually covers the summit of Horse Mountain, extending
southeast for a number of miles (Jenkins, 1962). The
study area is situated upon a truncated northwest-trending
ridge located directly east of the South Fork Mountain
Thrust Fault, a narrow belt of low-grade shist extending
south 300 miles along the Coast Ranges from the Oregon
border (California Division of Mines and Geology, 1966).
Basic drainage to the west of the study area is trellised, indicating that major streams are parallel to the structural grain of the area. Local, northwest- trending faults have created zones of weakness which are an important factor in the development of major drainage
channels, such as Redwood Creek and the Mad River (Figure
3, page 9). From a geomorphic standpoint, streams drain-
ing the study area and general region as a whole are
classed as geologically young, using criteria suggested by
Cotton (1958). The landscape, however, is classed as mature since well-defined ridge tops and divides are
commonplace. 13
Drainage and topography
From a hydrologic standpoint the study area is
located within the Klamath River Basin of the Pacific
Slope Basins Group of California. The nearest stream gaging station is located on Willow Creek approximately one-half mile west of the town of the same name. Another stream gage is located on the Trinity River near Hoopa
(United States Geological Survey, 1964). In reference to general drainage, the east slopes of Horse Mountain drain into the East Fork of Willow Creek, while west and south slopes drain into Redwood Creek. Ruby and Cedar
Creek empty into Willow Creek and provide major drainage from the ski area proper (Figure 4, page 20 ).
Rugged topography is characteristic of the north slopes of Horse Mountain, with slope steepness averaging
41 percent as determined from measurements obtained at snow sampling points (Table 9, page 114). Slope-induced topographic variation in the study area is therefore extreme, and elevations range from a minimum of 4,150 feet
(Figure 5, page 32) to a maximum of 4,951 feet on the summit of Horse Mountain. The average elevation of the study area is 4,608 feet (Table 9, page 114). 14
Aspect
North slope aspects in the study area are controlled by basin concavity. Thus, aspects are either northwest or northeast, with respective values ranging from north, 75 degrees west, to north, 85 degrees east
(Table 9, page 112). A comparison of mean west and east aspects in study basins indicates that the mean northwest aspect for the area is north, 38 degrees west, while mean northeast aspect is north, 46 degrees east.
Extremely steep slopes and north aspects minimize exposure of the ski area to solar radiation, which effectively reduces a major source of heat for snowmelt.
As an example of the effectiveness of steep north slopes in reducing solar radiation, Byram and Jemison (1943) report from a study in the Appalachians (34 degrees north latitude) that north slopes of 40 percent received only eight percent of the maximum intensity of solar radiation on December 21st (winter solstice), whereas slopes of 20 percent received 17 percent of maximum radiation intensity on the same date. Assuming similar elevation, the same general relationship would apply to the study area, except 15 that maximum radiation intensity would be slightly less
since the latitude of the study area is 40 degrees north.
Soil and vegetation
Soil formation in the study area is homogeneous due
to uniformity of parent material. Black (1964) reports
that serpentine rock forms the Montara soil series in
Humboldt County, a stony-clay loam of moderate perme- ability with good drainage. The shallow soil ranges in
depth from six to 18 inches and is characterized by
moderate potential for erosion hazard following material
disturbance of protective vegetative cover.
A noticeable diversity in vegetation exists on the
serpentinite soil that is prevalent on Horse Mountain.
The low quality soil supports a mixed stand of Jeffrey
pine (Pinus jeffreyi Grev. & Bafl.), western white pine
(Pinus monticola Dougl.), sugar pine (Pinus lambertiana
Dougl.), and Douglas-fir (Pseudotsuga menziesii Mirb. &
Franco). A list, noting by species all coniferous trees and common shrubs found in the study area is included in
Table 10 (page 115). 16
Aesthetic qualities
The aesthetic qualities of winter scenery on Horse
Mountain are inspiring. Near the summit of the mountain, scenery is enhanced by the presence of giant Jeffrey pines that have been contorted by the wind into scraggly and grotesque shapes, with crowns trailing to the northeast indicating prevailing wind direction during storm periods. On clear days the vista afforded from
Horse Mountain of the snow-clad Trinity Alps and Salmon
Mountains, as well as the summits of Mounts Shasta and
Lassen, contributes significantly to the inherent aesthetic value of the area.
Winter recreation facilities
Recreation facilities include three electric rope tows in the ski area with respective lengths of 500, 700, and 1,500 feet. Rope tows serve a total of 30.8 acres of ski slopes. A two-story ski lodge with cooking facilities and adequate room for overnight sleeping is located below
the intermediate slope (Figure 7, page 34). Operation of facilities is limited to weekends and holidays. 17
In addition to the above public facilities, six privately-owned warming cabins are located adjacent to the ski area. The combination of recreation facilities, excluding cabins, and including the cost of slope clearing, represent an initial capital outlay of $10,000 according to Dr. Walsh.
History of area
Methods
Historical information on winter recreation in the
Horse Mountain general area was obtained from Dr. Walsh and other longtime residents of the County. Useful information also was gleaned from a scrapbook of historical newspaper clippings compiled by the Humboldt
Ski Club.
Winter recreation use
In 1936, the founding of the Humboldt Ski Club by
Dr. Harold Carson of Eureka provided the major impetus in sparking enthusiasm for snow sport activities in Humboldt
County (San Francisco Examiner, February 8, 1953). From
1936 to 1949, skiing enthusiasts utilized the Titlow Hill area where a gasoline-powered rope tow was installed. In 18
1942, the Grouse Mountain Ski Lodge was in operation immediately south of Titlow Hill where a concessionaire provided meals and lodging for overnight skiers.
During periods of deep snow, skiers were required to trek eight miles southeast from Berry Summit to reach
the Titlow Hill area. From this standpoint the facilities
served a limited clientele, except when shallow snow permitted automobile access to the area over the poorly-
developed road. However, when access was possible, skiing
quality suffered because of inadequate snow. A limitation
of Forest Service funds prohibited development of improved access to the area during and immediately following World
War II (The Humboldt Times, January 30, 1947). Extreme
snowfall as low as elevations of 2,500 feet in 1950 and
1951 made access to the Titlow Hill area even more
difficult. During these years a portable rope tow was
operated by the Humboldt Ski Club near Berry Summit.
In 1951, the ski club realized the necessity for
development of a recreation area that would provide
reliable snow with improved accessibility. Having the
above in mind the club worked in cooperation with the
Forest Service to establish another ski area, named New 19
Prairie, near the headwaters of Cedar Creek (Figure 4).
Consequently, a short-term use permit was granted to the
Humboldt Ski Club by the Forest Service. Two rope tows and a cabin with overnight accommodations were in operation on the area until 1956. Protected north slopes on this site retarded snowmelt down to as low as 3,800 feet elevation. During the ensuing five years of operation of this area, the two miles of road from Berry
Summit to the turnoff below the ski area were usually kept free of snow by the County Road Department. However, skiers were often required to walk one-half mile to reach the slopes.
Because of frustrations resulting from questionable snowfall reliability and limited access that were inherent in the New Prairie area, the ski club was prompted to establish a slope located directly south of Horse
Mountain. In 1956 a rope tow was installed on this area, named Big Rock, and was operated until 1957 (Figure 4).
Reconnaissance of the current Horse Mountain Ski
Area began in 1957. On Horse Mountain, the advantages of guaranteed access, higher elevation, and diversified terrain on protected north slopes were recognized by the 20
Figure 4. General area map of Horse Mountain, illustrating access, bordering ownership, drainage, and location of historical skiing areas. 21
Humboldt Ski Club. Two rope tows were established on the slopes, and privately-owned cabins adjoining the ski area were improved to accommodate overnight skiers. Horse
Mountain quickly became the best developed of those ski areas mentioned previously and depicted in Figure 4
(page 20). In 1963, electric motors were installed to operate the tows and were recognized as a definite improvement over gasoline-powered engines which presented operational problems in cold weather.
In July of 1965, the Humboldt Ski Club requested the Forest Service to grant a transfer of permit to Dr.
Walsh, who then became financial administrator of the
Horse Mountain Ski Area. Construction of the two-story ski lodge was initiated during the same summer. Since
1965 the ski area has been managed by Dr. Walsh as a commercial enterprise, whereas previously the Humboldt
Ski Club functioned as a non-profit corporation. In the last 32 years, membership in the ski club increased from
25 to 200 members. During this period the use of all mentioned ski areas was limited to weekends and holidays. 22
Intensity of recreation use
During the last three years there were three times as many skiers using the Horse Mountain Ski Area as there were snowplayers (those engaged in activities other than skiing) recreating within the same general area (Table 1).
The average number of skiers per winter during the last five years was 1,709. For the same period the average number of snowplayers per winter was 600. According to
Dr. Walsh, gross receipts for use of rope tows on the ski area averaged $1,628 for the winters of 1965-1966 and
1966-1967.
Table 2 (page 24) provides statistics on winter recreation activity in the Lower Trinity Ranger District during the last 20 years, based on rope tow ticket receipts reported annually to the Forest Service by the
Humboldt Ski Club. The data reflect the use of the Horse
Mountain area as Horse Mountain was the sole winter sports area in the District during this period. The table indicates that in comparison to earlier years the number of participants in all winter sport activities has shown a marked increase since 1963. For example, from 1963 to 23
Table 1. Numbers of skiers and snowplayers who visited the Horse Mountain Ski Area from 1962 to 1967.a
NUMBER OF SKIERS NUMBER OF SNOWPLAYERS
Winter Total Visitor Total Visitor period days days
1962-1963 650 -- 400
1963-1964 2,395 2,395 1,000 500
1964-1965 1,300 1,300 400 200
1965-1966 2,000 2,000 500 250
1966-1967 2,200 2,200 700 350
MEAN 1,709 1,974 600 325
a From United State--Forest Service, 1962-1967. Numbers of skiers are based on rope tow ticket receipts. Numbers of snowplayers were estimated by the Humboldt Ski Club. 24
Table 2. Number of participants in all winter recreation activities from 1947 to 1966 in the Lower Trinity Ranger District of Six Rivers National Forest.a/
a/Fromar Number of Number of Average length year visitors visitor days of visit in days
1947 300 600 2.00 1948 410 615 1.50 1949 800 800 1.00 1950 1,650 1,650 1.00
1951 1,650 825 0.50 1952 2,062 1,031 0.50 1953 950 425 0.50 1954 2,000 1,000 0.50
1955 690 345 0.50 1956 1,000 1,000 1.00 1957 1,200 1,200 1.00 1958 600 600 1.00
1959 500 500 1.00 1960 1,700 1,700 1.00 1961 2,400 2,400 1.00 1962 800 800 1.00
1963 1,100 1,000 1.00 19 64 4,000 2,900 0.72 1965 3,500 2,500 0.73 1966 3,200 3,200 1.00
ANNUAL MEAN 1,526 1,255 0.92
a/From United States Forest Service, 1947-1966. Annual values were based on rope tow ticket receipts. 25
1966 the average number of skier days was 2,950, compared to 790 for the period from 1947 to 1950. This represented nearly a four-fold increase in intensity of use. During the last five years visitation increased 65 percent in relation to an average annual use of 1,526 skier days during the last 20 years. The average length of visit was maintained at approximately one day (0.92) because of limited overnight accommodations on most of the earlier skiing sites.
Climatic history
Climatic data for Horse Mountain other than snow depth are not available. Temperature and rainfall data are available from nearby Honor Camp 42 and Salyer
(Figure 3, page 9).
Snowfall data were obtained from three sources:
(1) newspaper clippings of ski club activities, (2) Dr.
Walsh, who has skied in Humboldt County since the early
1940's, and (3) snow survey data from the Big Flat area of Trinity County, located 40 miles northeast of Horse
Mountain (Figure 3, page 9). Snow data obtained by the
Forest Service at Big Flat (Table 11, page 116) were used in evaluating skiing potential on Horse Mountain from 1946 26
to 1966 during months of February through May. Months
with snow depth in excess of 18 inches were interpreted
as favorable periods for skiing on Horse Mountain
(Table 3).
Although Big Flat is only 150 feet higher in
elevation than Horse Mountain, certain physical and
geographical factors caused the extrapolation of data
from this area to reflect an underestimate of potential
for Horse Mountain. Skiing potential was underestimated
since the mean annual precipitation of the Big Flat area
from 1905 to 1955, as determined from isohyets, was 60
inches, compared to 80 inches for the Horse Mountain area
(California Department of Water Resources, 1968). Higher
precipitation on Horse Mountain is caused by southwest
storm movement occurring directly from a marine environ-
ment, with acute orographic uplift and cooling of
moisture-laden air passing over the mountain crest.
A storage gage on Boardcamp Mountain (Figure 3,
page 9), at an elevation of 4,500 feet and situated 12
miles south of Horse Mountain, recorded a mean annual
precipitation of 105.54 inches from 1963 to 1967
(California Department of Water Resources, 1968). These 27
Table 3. Evaluation of skiing potential on Horse Mountain from 1946 to 1967 during months of February to May.
Probable maximum General evaluation Year snow depth in inches a/ Datea/ of skiing potentialb/ 1946 85.5 2-26 Feb. & Mar. good 1947 18.8 2- 1 poor year 1948 28.8 3-26 March good 1949 69.2 3-27 Feb. & Mar. good 1950 56.5 3-27 Feb. & Mar. good 1951 54.5 3- 6 Feb. & Mar. good 1952 124.7 3-24 Feb. - Apr. good 1953 60.0 2- 1 Feb. - Apr. good 1954 76.7 2- 1 Feb. & Mar. good 1955 53.4 2-28 Feb. & Mar. good 1956 116.9 3- 1 Feb. - Apr. good 1957 37.3 1-31 February good 1958 118.9 4- 2 Feb. - Apr. good 1959 74.9 2-27 Feb. & Mar. good 1960 53.6 3- 1 Feb. - Apr. good 1961 26.0 4- 4 April good 1962 128.0 3- 1 Feb. - Apr. good 1963 21.9 4- 4 poor year 1964 54.9 1-30 Feb. & Mar. good 1965 43.5 1-28 Feb. & Mar. good 1966 92.2 3- 3 Feb. - Apr. good / 1967 66.8 4-30 Feb. - May goods
MEAN 66.5
From snow survey data obtained in Trinity County (Table 11, page 116). Maximum depths from survey were adjusted by 33 percent (see page 28) to compensate for the pre- cipitation disparity between Horse Mountain and Big Flat. b/Months when snow depth from Big Flat (Table 11, page 116) exceeded 18 inches signified more than 18 inches on Horse Mountain, and hence provided good skiing. c/Maximum depth in study basins during 1966-1967 was used. 28 data were not used as a basis for Table 3 (page 27) because of the short measurement period. Boardcamp
Mountain represents the only precipitation station in
Humboldt County that is located above 2,500 feet and is certified in annual climatological reports by the United
States Weather Bureau and the California Department of
Water Resources.
Snow survey data were used to estimate probable maximum snow depth on Horse Mountain from 1946 to 1967.
Because of the precipitation disparity of 33 percent between the two areas, maximum annual snow depths for Big
Flat were increased by the same, and resulting values were assumed to approximate seasonal maximum snow depths for Horse Mountain (Table 3, page 27). This assumption was based on comparison of snow depth on Horse Mountain and on Big Flat in 1967 showing differences close to 33 percent during the only two times when sampling dates were similar between both areas. For example, snow depth on April 2nd in the undeveloped basin on Horse Mountain
(49.7 inches) exceeded the snow depth for Big Flat on
April 4th (37.4 inches) by 32.9 percent. In addition, the snow depth on Horse Mountain on April 30th (66.8 29 inches) exceeded the snow depth for Big Flat on April
28th (45.8 inches) by 45.8 percent. Unfortunately the two day lapse between sampling dates limited the validity of comparisons. However, errors were minimized as no more than 0.30 inches of precipitation was deposited on
Horse Mountain during either lapse between the two sampling dates. This amounted to approximately two inches of snow depth using the average snow density found in this study.
In summation, the data (Table 3, page 27) suggest that during the 22 winter periods from 1946 to 1967, all but five provided at least two months of skiing on Horse
Mountain. During eight seasons snowfall was adequate to
offer three months of skiing. In addition, February and
March were the most reliable for providing snowfall in quantities sufficient to permit skiing. Probable maximum snow depth during the last 22 years ranged from a low of 18.8 inches in February of 1947 to a high of 128 inches in March of 1962. Annual average maximum depth during the 22 year period was 66.5 inches.
Cooperative snow surveys were initiated by the
Department of Water Resources in late January. Thus, 30 no data are available for November, December, and January.
According to members of the Humboldt Ski Club, snowfall was seldom sufficient to provide skiing in November and early December during the last 20 years on Horse Mountain.
Known and estimated snow depths for the Horse
Mountain general area as obtained from newspaper clippings and interviews are included in Table 12 (page 117). As far as the author has been able to ascertain, this information represents the only quantitative data that exist for the area, and it was appended for this reason.
To the extent that reported measurements do not refute or conflict with extrapolated data, snow depths in Table 12
(page 117) are consistent with depths obtained from snow surveys at Big Flat. STUDY METHODS
Definition of study basins
Using aerial photographs, study areas were partitioned into a developed basin and an undeveloped basin (Figure 5) with respective areas of 63.4 and 64.0 acres in each basin. The southern boundary of the developed basin was located near the summit of Horse
Mountain. The northern boundary was established immedi- ately below the 1,500 foot rope tow, since dense timber below this point prohibited location at a lower elevation level. The eastern boundary was located with an allowance of 300 feet of forest between the boundary and adjoining ski slopes, to permit snow sampling of forest adjacent to ski slopes. The western boundary was located with the same intent, but forest areas located adjacent to the ski lodge were skirted to eliminate bias in snow sampling resulting from heavy foot traffic. Natural openings and openings created by timber extraction in the developed basin during the last five years have provided the ski 32
Figure 5. Topographic map of the Horse Mountain Ski Area, showing the study basins, snow sampling points, and other detail features extracted from August, 1966 aerial photographs of 1/12,000 scale. 33 slopes. Forest within the developed basin remains in blocks amounting to 32.6 acres (Figure 5, page 32).
All boundaries of the undeveloped basin, except the northern boundary, were located to conform to the natural basin drainage. The northern boundary was estab- lished along the lowest contour level of elevation accessible to snowshoe travel in an attempt to account for variation in snow depth within the basin related to elevation change. Historically, the undeveloped basin has remained essentially undisturbed except for construction of the unimproved fire access road depicted in Figure 5 (page 32). Future recreation plans on Horse
Mountain include the development of this basin by the
Humboldt Ski Club for skiing purposes in the next 10 to
15 years. Comparisons of snowfall accumulation and retention between the undeveloped and developed basin are essential from a recreation use standpoint to determine if the undeveloped basin accumulates and retains significantly more or less snow than the developed basin.
Photographic examples of physical features in each study basin are illustrated in Figures 6 through 9. 34
Figure 6. Developed basin as seen from the northeast on February 4, 1967 from snow sampling point number three (elevation 4,350 feet). Note the insufficient snow cover on nearest ski slope.
Figure 7. Humboldt Ski Club lodge located below intermediate slope in the developed basin. Note rope tow in center foreground. Mean depth of snow on slope was 60 inches (April 30, 1967). 35
Figure 8. Undeveloped basin as seen from the northeast on April 2, 1967 from snow sampling point number 43 (elevation 4,400 feet). Mean depth of snow in basin was 50 inches.
Figure 9. Undeveloped basin near snow sampling point number 44 (elevation 4,440 feet). Note the group of young western white pine (Pinus monticola) in foreground. Mean depth of snow in basin was 20 inches (February 4, 1967). 36
The weather station
Location and establishment
On October 22nd, 1966, a weather station was established in a natural opening on the ridge between the two study basins at an elevation of 4,820 feet (Figure 5, page 32). Establishment of the weather station on the ridge was done with the expectation that such a location would reflect the average climatic conditions existing between the two study basins. Access by truck to the site during fall facilitated easy transport of materials and instruments. During winter, remoteness of the location reduced the probability of site disturbance or vandalism occurring to the weather station.
Instrumentation
On October 22nd a standard rain gage, snow depth marker, and maximum-minimum thermometer were installed at the weather station. On December 3rd a recording hygrothermograph was installed to provide measurements of humidity and temperature, and on January 14th, a weighing type recording rain gage equipped with alter shield was 37 added. A small weekly charge of an ethylene glycol type of antifreeze solution (Prestone) was used and proved effective in preventing frozen precipitation catches in both rain gages. In addition, a few drops of lightweight motor oil (RPM 20-30) were poured on the surface of the antifreeze solution to assure minimum evaporation losses from the mixture of antifreeze and precipitation.
In addition to the above instrumentation, a recording pyrheliograph was installed on February 2nd for use in measuring incident solar radiation in units of gram calories per square centimeter per minute
(langleys). The measuring element of the instrument consisted of two identical bimetallic strips, one of which was blackened while the other was highly polished and covered with a shield. The blackened strip was exposed to both the ambient temperature and the radiant energy. Mounting of the measuring element was such that only the differential temperature between the strips caused the recording pen to move, while the movement of the strips due to ambient temperature fluctuation caused no movement of the pen. A maximum instrument range of three langleys provided a comfortable margin over the 38 maximum solar radiation encountered, and concentrated the most commonly recorded values to midscale where the highest degree of instrument accuracy exists. The borosciate glass dome mounted on the case top of the pyrheliograph permitted a transmission coefficient of approximately 90 percent for all wave lengths from 0.36 to 2.0 microns, a range which includes most solar radiation reaching the earth (Belfort Instrument Company,
1965).
To measure temperature fluctuation at the soil and snow surface, a recording double distance thermograph was located in a special shelter immediately to the east of the weather station on February 12th. One probe of the thermograph was situated at the soil surface level and the other on the snow surface, with adjustment of the latter made following each storm. Probes of another thermograph were situated at depths corresponding to one-third and two-thirds of the total snow depth on the date of establishment. These probes were left undisturbed throughout the winter except for two adjustments in March and April as snow depth increased. Their purpose was to determine if temperature fluctuation existed within the snow pack at any time. 39
Unfortunately, an anemometer was not available for this study. Recorded measurements of wind velocity would have permitted a more comprehensive correlation of measured climatic parameters to snow melt. The weather station was maintained weekly from October 22nd to June 4th, with measurements recorded and charts changed either on Saturday or Sunday. Photographs of the completed weather station are in Figures 10 and 11.
Snow quality
Snow quality measurements were obtained from an opening located to the east of the weather station.
Snow quality refers to the percentage of snow by weight which is in the form of ice, and in this study the index provided a quantitative expression of the suitability of the snow pack for skiing since qualities below 85 percent produced a surface layer of slush on ski slopes that yielded poor skiing. More specifically the index is used to evaluate snow pack stability. Snow quality samples were taken weekly at locations corresponding to one-third and two-thirds of the total snow depth on the sampling 40
Figure 10. Weather station as seen from the southwest, illustrating recording rain gage and fabricated alter shield, with pyrheliograph attached in rear. Note standard rain gage attached to left corner of protective fence. Hygrothermograph and maximum- minimum thermometers were located in the main weather box.
Figure 11. Weather station as seen from the northeast on April 30, 1967 when snow depth attained a seasonal maximum of 87 inches. Note that fence was covered by snow. 41 date, with two samples removed at each depth so that a total of four samples were tested weekly.
The calorimetric method was used to compute snow quality (Bernard and Wilson, 1941). A sample of snow was inserted into a thermos bottle partly filled with hot water. From initial and final temperatures and known weights (or volumes) of water and snow, snow quality was computed by using the following formula (Linsley et al., 1949).
(T1 - T2)(W1) (T2 - 32)W2 Qt 1.44W2 where: Qt = snow quality in percent. T = temperature of hot water in degrees F. 1 T = final temperature of mixture of warm water 2 and snow sample in degrees F.
W = weight of hot water in pounds. 1
W2 = weight of the snow sample in pounds.
The above formula usually employs the addition of a calorimeter constant to the weight of hot water (W1) to compensate for error resulting from instrument heat loss. The thermal loss is computed by multiplying the 42 mass of the calorimeter (thermos bottle) by the specific heat of the material from which it is constructed.
However, the constant was eliminated in this study since the use of a glass thermos bottle during measurement reduced heat loss to a negligible level (Ingersoll et al., 1953).
Snow sampling points
Sample size
A number of factors determined the sample size used in this study. Preliminary snow sampling in early
December indicated a large variability in snow depth within each basin. Thus it was uncertain that basins could be statistically compared as single units unless a large sample size was used. However, variation among measurements on ski slopes or within particular blocks of timber indicated minor variability, with large enough differences between sample means to permit significant statistical comparison of areas within basins at the
10 percent level of acceptance.
The Humboldt Ski Club indicated a need for measurements from as many areas as possible in both basins, while expressing a particular interest in the 43 developed basin. As a compromise between the statistical application and the practical use that would be made from snow measurements, the number of sample points repre- senting the physical limitation of measurement in a day's work was selected as a sample size. Thus, 45 sample points were selected for the study.
Particular emphasis was given to the developed basin where 30 sample points were selected. Since the acreage held in ski slopes and forest within the developed basin was nearly equal (30.8 and 32.6 acres respectively)
15 sample points were selected for each of the two types of terrain. The remaining 15 points were selected for the undeveloped basin.
Method of selection
Sample points were chosen using a one-fourth inch grid overlayed on aerial photographs (1966) of 1/12,000 scale with delineated study basins. The grid was numbered at the intersection of lines and numbers were chosen at random without replacement. Each chosen number repre- sented a sample point, and its location was pricked on the aerial photograph for later location and permanent establishment on the ground. 44
Criteria for rejection of sampling points were established. Points that landed within tree centers or on rope tows were rejected. Points that were intended to represent ski slope sample points were rejected if they were less than 20 feet from the edge of the forest margin.
Similarly, forest points were rejected if they were less than 20 feet from the edge of ski slopes. Therefore, edge characteristics were not sampled in this study since measurements would have masked the variation between open and forested areas that was desired for comparative statistical analysis.
Method of establishment
Sample points were permanently established by means of a numbered, metal tag attached to a tree near
the location of each point on the ground. Slope distance and compass bearing from the tree to the point was
obtained using a hand compass and 50-foot cloth tape.
The following variables were measured at the location of each sample point and are recorded with compass bearings and distances in Table 9 (page 112): elevation, aspect, percent slope, and percent of crown canopy within a
75-foot radius circle (2/5 acre) from the sample point. 45
These variables were measured to allow for correlation of physiographic features in each basin with snowfall accumulation and retention. Other variables, such as height of dominant vegetation and basin concavity, may have been important, but were not measured since Anderson
(1957) does not emphasize their significance in affecting snowfall accumulation and retention. All sample points were established by December 22nd (Figure 5, page 32).
Compass bearings and aspects were measured with a pocket compass, and an altimeter and topographic map were used to determine elevations. A topographic abney was used to measure slope. Crown canopies within the
75-foot radius circle were measured from 1966 aerial photographs (1/12,000 scale) using the Meyer dot crown count method (Meyer and Worley, 1955). In using this method, plot areas were delineated by a frosted celluloid overlay with holes representing 2/5 of an acre. A clear celluloid strip with five dots evenly spaced in such a manner that they fitted into the plot area at five equally spaced positions with four movements was used.
Crown cover percent was determined by the number of dots that fell on tree crowns within each plot divided 46 by the total number of dots (20) obtained from the four movements within the plot.
Measurement
A five-foot radius circle constituted the sampling area surrounding each established point on the ground.
During periods of measurement, snow core samples were extracted and weighed at each point using the Mount Rose snow sampler. The sampler consists of a duraluminum tube in 30-inch sections with an interior diameter of 1.485 inches, and is provided with a cutter section to aid in penetrating ice planes and dense snow. The diameter of the tube is such that one ounce of weight is equivalent to one inch of water. Slots in the side of the tube and graduations on the outside permit measurement of the snow depth and length of core removed. Core length is usually slightly less than snow depth because of settling of snow within the tube as the sampler is inserted into and extracted from the snow profile. For a more complete description of the Mount Rose snow sampler, the reader is referred to Linsley et al. (1949).
Two samples were obtained from each sample point to diminish measurement variability. Snowshoes were worn 47 while sampling during periods of melting to minimize site disturbance and bias resulting from snow compaction.
Measurements were obtained from January 7th until May
21st as weather permitted. An example of the type of snow survey data sheet used in this study is in Table
13 (page 118). DISCUSSION OF RESULTS
Analysis of individual storms
Individual storms during the study period were analyzed to separate rainfall from snowfall (Table 15, page 120). The separation was determined by correlating temperature recorded on the thermograph charts with precipitation collected in the recording rain gage.
Numerous field observations indicated that precipitation falling when the air temperature was 34 degrees or lower was snow, whereas precipitation with temperatures above
34 degrees yielded sleet or rain. Thus, readings from precipitation charts were converted to snowfall when temperature charts for the same period indicated temper- atures at 34 degrees or lower. The intent of this analysis was to measure snowfall only, with periodic snow sampling within basins providing an estimate of snow retention. Snowfall with air temperatures one or two degrees above 32 degrees is not uncommon, and snow has been known to fall through shallow layers of warm 49 air having temperatures higher than 50 degrees at the ground surface (McAuliffe, 1929).
A minimum allowance of 24 hours of non-recorded
precipitation was used to segregate storms, with a storm defined as any period yielding measurable precipitation.
Twenty-four hours was used as a separation point between
storms instead of a shorter period because daily weather maps and precipitation charts indicated that precipitation
was essentially uninterrupted once it began.
Description of 1966-1967 winter
Climatic conditions on Horse Mountain prior to the first measurable snowfall were characterized by low rainfall and warm days. From September first until
October 22nd approximately 1.25 inches of rain were deposited on Horse Mountain as estimated from rainfall data recorded in Salyer. Before the first measurable snowfall of November 6th, 0.30 inches of rain accumulated at the weather station after October 22nd. During the same period, the average weekly maximum temperature was
75 degrees, and the average weekly minimum was 45 degrees.
The initial snowfall of two inches on November 6th 50 persisted on the ground for 12 hours, with the snow line established at an elevation of 3,700 feet.
During November, 10.74 inches of rain, or 36 percent of the 29.43 inches of rain measured during the study period was collected (Table 14, page 119). Only
13 percent of the November precipitation of 12.39 inches was snowfall. November 30th marked the beginning of continuous measurable snow cover on Horse Mountain, a snow cover which persisted until May 28th.
December was similar to November in that precipi- tation was primarily in the form of rain. During this month, 14.30 inches of precipitation were recorded, 74 percent of which was rain. A 12-inch increase in snowfall over that in November was due in part to cooling, in addition to the higher precipitation. In December, storms of short duration at infrequent intervals permitted intensive nighttime radiation cooling on shaded north slopes. Snow-covered slopes were coated with an ice crust that was one-half inch thick throughout most of the month due to subfreezing nights with resultant cold air drainage. 51
Total precipitation in January was nearly the
same as that of November and December, but in contrast,
72 percent of the total January precipitation of 14.30
inches was snow. From January 6th to January 18th the
persistent presence of the Pacific High Pressure Cell
located directly off of the northern California coast
created a period of temporary drought in Humboldt County.
During the interim, snow depth at the weather station
decreased from 17 inches to a monthly low of 12 inches.
Precipitation in January was concentrated in the 13-day
storm period lasting from January 19th to January 31st
(Table 15, page 120). During this storm 58 inches of
snow were recorded, but the effective contribution to
snow depth was only 21 inches since 4.05 inches of warm
rain fell sporadically during the same period.
During early February the Pacific High effectively
diverted the main storm track northward. Consequently,
no precipitation occurred on Horse Mountain from February
1st until February 13th. In addition, only two storms of
very light intensity occurred during the remainder of the
month, yielding 0.97 inches of precipitation, all in the
form of snow. Historically, statewide February 52 precipitation approached that of February 1964, when the
California average was only five percent of normal for a
30-year period (California Department of Water Resources,
1967). During the drought the stationary Pacific High effected dry north winds which created a general warming period. Average minimum and maximum temperatures were noticeably higher in February than during any month from
December through April (Table 19, page 125). As a result, snow depth at the weather station decreased from a monthly maximum of 24.5 inches on February 2nd to a monthly low of 16 inches on February 13th.
In contrast to a relatively dry and warm February,
March was characterized by heavy snowfall and low temperature. During this month, three storms deposited
47 inches of snow on Horse Mountain, raising the snow depth to 57 inches on April 2nd. The most intense storm of the winter occurred from March 9th to March 20th, when an increment of 28 inches of snow was measured at the weather station. The intense storm resulted from the presence of a deep low pressure trough centered to the west of Vancouver. The presence of the Pacific High to the south of the trough and another high pressure area 53 to the east of Vancouver forced the low pressure cell to remain stationary (Figure 12). During the ensuing six days of relative immobility, the low pressure trough functioned similar to an enormous pump, drawing in moist, cold air from the Gulf of Alaska with sufficient magnitude to provide heavy snowfall throughout Oregon and California above 3,000 feet in elevation. Another storm system of similar structure deposited an additional 15 inches of snow on Horse Mountain during the last week in March.
April was the coldest month of the winter on Horse
Mountain. Thermograph data revealed that the temperature exceeded 32 degrees (F.) only 11.8 percent of the time from April 1st to April 30th (Table 19, page 125). The seasonal minimum temperature of 17 degrees was recorded on April 18th. Low temperatures resulted from a low pressure trough off of the California coast which routed a continuing series of arctic-origin storms across the state, yielding measurable snowfall during 23 of the 30 days in April. Cold April temperatures prompted heavy snow retention in the north coastal area of California.
Flows in snowfed tributaries of this area, such as the
Trinity River, were only 75 percent of their respective 54
Figure 12. General weather pattern in the western United States on March 13, 1967. 55
30 year normal for the month (California Department of
Water Resources, 1967). April precipitation totaled
7.92 inches, 99 percent of which was snow. From April
2nd the snow depth at the weather station increased to a seasonal maximum of 87 inches on April 30th (Figure
15, page 67).
The series of arctic-origin storms ended on May
1st, and on this date the spring thaw commenced. Only one snowstorm occurred in May, from the 9th to the 12th, yielding 13 inches of snow. All remaining snow on the ground near the weather station melted on May 28th when
0.30 inches of rain was collected. However, a few patches of snow, some six inches in depth, remained in both study basins as late as June 4th.
In retrospect, from October 22nd until June 4th,
24 separate storms yielded measurable precipitation on
Horse Mountain. Precipitation was recorded during 104 days from a possible 226 days, or during 46 percent of the days in the above period. Mean rainfall per storm was 1.22 inches as compared to 1.43 inches water equiv- alent, or a mean snow increment of 8.4 inches per storm
(Table 15, page 121). The snowline was located at an 56 average elevation of 3,300 feet during the 17 storms that yielded measurable snowfall.
Weather station analysis
Humidity
Daily hygrometer data were compiled and analyzed to determine the length of time that humidity measured
100 percent in order to determine storm duration.
Humidity readings of 100 percent were correlated with weekly precipitation in the standard rain gage to determine storm duration (Table 15, page 120) prior to the establishment of the recording rain gage. This method was later checked out and proven accurate during a number of storms after the recording rain gage was installed. However, during severe storms, the delicate hairs on the hygrometer often became wet and retained humidity readings at 100 percent considerably longer than the actual storm duration computed from the recording rain gage charts.
As Table 4 indicates, April was characterized by the highest average daily humidity (93 percent), whereas
February was the least humid with an average daily reading 57
Table 4. Relative humidity measurements on Horse Mountain during the winter of 1966-1967.
Mean daily humidity Percent of time that Month in percent humidity was 100 percent
December 76.0 49.7
January 71.4 39.7
February 60.5 23.1
March 81.4 49.5
April 93.0 61.8
May 65.9 15.2
MEAN 74.7 39.8 58 of 60.5 percent. These results were anticipated since the number of days of measurable precipitation during the study period were the most numerous in April (23 days) and the least numerous in February (5 days).
Temperature
A comparison of mean daily temperatures on Horse
Mountain with temperature data recorded at Honor Camp 42
(elevation 1,875 feet) for the last seven years provided sufficient data to compute a short-term temperature curve for Horse Mountain (Figure 13). The hypothetical curve indicated that study period measurements on Horse Mountain were slightly above normal during February and May, and were well below normal during April, since the mean monthly April temperature was 11 degrees below the hypo- thetical curve. April temperature was not used in computing the hypothetical curve because seasonal curves
(December through May) noticeably diverged during this month and the reading would have biased the analysis.
Because of the elevation difference of 2,945 feet between the two weather stations, as was expected, Horse Mountain temperatures ranged from 5.5 degrees (January and
February) to 11 degrees (April) lower than temperatures from Honor Camp 42 during the study period. 59
MEAN MONTHLY TEMPERATURE ON HORSE MOUNTAIN, 1966-1967 (ELEV. 4,820 FT.)
MEAN MONTHLY TEMPERATURE AT HONOR CAMP 42, 1966- 1967 (ELEV. 1,875 FT. )
HYPOTHETICAL MEAN MONTHLY TEMPERATURE ON HORSE MOUNTAIN FROM 1961 TO 1967 (CURVE ESTABLISHED BY COMPUTING MEAN DISTANCE BETWEEN ABOVE CURVES FOR ALL MONTHS EXCEPT APRIL, THEN SUBTRACTING FROM CURVE BELOW)
MEAN MONTHLY TEMPERATURE AT HONOR CAMP 42 FROM 1961 TO 1967
Figure 13. Comparison of mean monthly temperature on Horse Mountain (1966-1967) with mean monthly temperature from Honor Camp 42 from 1961 to 1967 (From Tables 17 and 19, pages 123 and 125). 60
Additional temperature information compiled from
recording thermograph tracings is in Table 19 (page 125).
Further analysis of the charts exposed the arctic
tendencies of the study area as indicated by an average
temperature of 36.9 degrees from December through May.
Additionally, the temperature was below 32 degrees
approximately 41 percent of the time during this six
month period.
Snow density
The density of freshly-fallen snow was measured at
the weather station on a number of occasions throughout
the winter to determine the percentage of the snow volume
occupied by its water equivalent. Measurements were
obtained with the snow sampler immediately following
storms that provided a measurable increment of fresh snow.
For density evaluation, increments in excess of 10 inches were required in order to provide the highest degree of accuracy while weighing the sampling tube, since the
sensitivity of the instrument did not lend itself to small measurements and all small measurements that were tested
yielded unreasonably high snow densities. 61
Snow density showed little seasonal variability from December to April, although the January measurement was low in comparison to other months (Table 5). The average of 17 percent was slightly higher than values reported by other authors. For example, Linsley et al.
(1949) report that freshly-fallen snow usually has a density between seven and 15 percent, with an average of about 10 percent. Other authors, such as Wisler and
Brater (1965) and Butler (1957), indicate that fresh snow has a density of about 10 percent. However, densities ranging from six to 34 percent have been recorded by
Rikhter (1954) from an intensive snow study in Illinois.
Average density was used in conjunction with recorded precipitation and temperature data to compute the total seasonal snowfall of 201.9 inches (Table 14, page 119). This technique proved to be more reliable than the use of weekly snow increment tallies obtained from the snow depth marker, since the degree of subli- mation and settling of the snow cover between measurements was unknown. Mean density of the total snow cover from
November through May was 43.6 percent (Table 16,page 122). 62
Table 5. Periodic density measurements of freshly-fallen snow1966-1967. on Horea/ Mountain during the winter of
Depth of Water Density Date freshly-fallen equivalent in percent snow in inches in inches
December 8 9.0 1.5 16.7
January 21 11.0 1.5 13.6
March 11 23.5 4.5 19.1
April 1 15.0 2.5 16.7
April 16 13.5 2.5 18.5
TOTAL 72.0 12.5 MEAN 17.0
a/Obtained near the weather station snow depth marker.
b/ — Computed by dividing the water equivalent by the depth of freshly-fallen snow, multiplied by 100. 63
Precipitation
From October 22nd to June 4th the total measured precipitation on Horse Mountain was 63.76 inches.
Precipitation was almost evenly divided between rainfall and snowfall with respective values of 29.43 and 34.33 inches for each (Table 14, page 119). From June 4th to
October 22, 1967, total precipitation recorded in Salyer was 2.07 inches (United States Department of Commerce,
1967). Thus it is highly probable that total precipi- tation on Horse Mountain during the above 365 day period did not exceed 70 inches. In comparison with the
Department of Water Resources isohyetal map, total precipitation for 1966-1967 was therefore 13 percent
(10 inches) below the 50 year normal of 80 inches for the area.
Other evidence indicated that precipitation on
Horse Mountain was below normal from November 1966 through
May 1967. In Figure 14, recorded precipitation for the above period was plotted against mean monthly precipi- tation data recorded in Salyer (elevation 623 feet) during the last 19 years. As determined from the graph, 64
MONTHLY PRECIPITATION ON HORSE MTN., 1966-1967 (ELEV. 4,820 FT.). TOTAL (NOV.-MAY) WAS 63.28 INCHES.
MONTHLY. PRECIPITATION IN SALYER , 1966-1967 (ELEV. 623 FT.). TOTAL (NOV.-MAY) WAS 42.00 INCHES.
HYPOTHETICAL MEAN MONTHLY PRECIPITATION ON HORSE MTN. FROM 1949 TO 1967 (CURVE ESTABLISHED BY COMPUTING MEAN DISTANCE BETWEEN ABOVE CURVES FOR MONTHS OF NOVEMBER, DECEMBER, MARCH AND APRIL, THEN ADDING TO CURVE BELOW ). MEAN TOTAL (NOV - MAY) WAS 77.80 INCHES.
MEAN MONTHLY PRECIPITATION IN SALYER FROM 1949 TO 1967. MEAN TOTAL (NOV.-MAY) WAS 45.11 INCHES.
Figure 14. Comparison of monthly precipitation on Horse Mountain (1966-1967) with monthly precipitation in Salyer from 1949 to 1967 (From Tables 14 and 17, pages 119 and 123). 65 precipitation on Horse Mountain exceeded the mean monthly precipitation in Salyer by approximately two to four inches during all months except February. Considering the spacing and slope of both lines in the graph, the obvious conclusion is that precipitation on Horse
Mountain during February was well below normal, especially since precipitation in Salyer during 1966-1967 was similarly below normal during the same month. February precipitation was only eight percent of the 12 inch normal as determined from the long-term hypothetical curve.
Further use of this curve indicated that mean total precipitation on Horse Mountain from 1949 to 1967
(November through May) was 77.80 inches. This value compared closely with the 50 year normal (12 month) of
80 inches cited by the California Department of Water
Resources. Precipitation for January, February, and May were not used in computing the hypothetical curve because seasonal curves (November through May) noticeably converged during these months, and the inclusion of these respective readings would have lowered the hypothetical curve further and yielded a total precipitation of only
66.00 inches, which is unrealistic when compared to the 66
80 inches cited by the California Department of Water
Resources. The method that was used yielded a total that was much closer to 80 inches.
When Horse Mountain snow depths were related to measurements from Big Flat and Anthony Peak, with the latter located 75 miles southeast of the study area
(Figure 3, page 9) at an elevation of 6,200 feet, the plotted curves confirmed two facts: 1) February snow depth on Horse Mountain was significantly below normal and 2) snow depths on Horse Mountain were significantly above normal during April, since the maximum April measurement (87 inches) exceeded the normal April depth on Anthony Peak by 37 inches (Figure 15). Therefore, a logical conclusion is that the maximum April snow depth at the weather station in 1967 was at least three feet above normal. Because precipitation was only slightly above normal during March and April (Figure 14, page 64), extreme snow depth during these months was related more directly to snow retention associated with low temperature than to gross accumulation of snow.
The importance of elevation in regulating snowfall is well illustrated in Figure 15 since snow depths on 67
SNOW DEPTH ON HORSE MTN., 1966-1967 (EL. 4,820' ) SNOW DEPTH AT BIG FLAT, (TRINITY COUNTY -EL. 5,100 ) MEAN SNOW DEPTH AT BIG FLAT FROM 1946 TO 1967 SNOW DEPTH ON ANTHONY PK., 1967 (TEHAMA COUNTY-EL. 6,200' ) MEAN SNOW DEPTH ON ANTHONY PK. FROM 1946 TO 1967
Figure 15. Snow depth fluctuation at the Horse Mountain weather station during the winter of 1966-1967 with comparative depths during months of data avail- ability from the nearest permanent snow survey courses (From Tables 11, 16 and 18). 68
Anthony Peak in 1967 exceeded measurements from Big Flat and Horse Mountain during all months for which data are available. The higher elevation undoubtedly caused a large proportion of precipitation to fall as snow since the normal precipitation on Anthony Peak is only 60 inches
(California Department of Water Resources, 1968).
Snowfall at the weather station showed a marked increase throughout March and April as indicated in Figure
15 (page 67). From March 4th until April 30th the snow depth increased from 20 inches to a seasonal maximum of
87 inches, or from a water equivalent of 9.5 inches to
30.5 inches (Table 16, page 122). Comparative photographs of snow depth for November and April are in Figures 16 and 17.
Solar radiation
A high degree of correlation was found to exist in relating the variation of mean daily temperature to weekly solar radiation from February to May (Figure 18, page 70).
Analysis of the above by the least squares method of linear regression yielded a correlation coefficient of
0.9316. Thus, the coefficient indicated that 86.8 percent [(0.9316)2 x 100] of the variation in mean daily 69
Figure 16. Snow depth marker located immediately south of the weather station indicating a snow depth of one inch on November 20, 1966.
Figure 17. Snow depth of 76 inches on April 22, 1967. 70
WEEKLY SOLAR RADIATION IN LANGLEYS Figure 18. Relationship of mean daily temperature per weekly period to weekly solar radiation during the period from February 11th to June 2nd on Horse Mountain (From Table 20, page 126). 71 temperature (weekly period) can be accounted for by the linear relationship between weekly solar radiation and mean daily temperature, with the remainder of the variation accounted for by the interrelationship of other climatic factors.
The practical application of the regression is that it facilitates computation of either variable for use in theoretical snowmelt formulae by using only one instru- ment, i.e. either a recording thermograph or pyrhelio- graph. Pyrheliographs are costly in comparison to recording thermographs and are highly susceptible to damage. Therefore, the advantages of obtaining radiation values by use of thermograph data in conjunction with a regression graph are realized not only from an economic viewpoint, but also from the standpoint of availability of instrumentation, since most established weather stations possess a recording thermograph that could be used once a basic regression graph was established.
Correlation of solar radiation to snowmelt
Solar radiation is one of the three major sources of heat for snowmelt, the other two being air convection and vapor condensation (Butler, 1957). In computing 72 radiation snowmelt, an average albedo (incident radiation reflectivity of snow) of 80 percent was assumed. Clean, dry, freshly-fallen snow has an albedo of about 90 percent
(Reifsnyder, 1965). During most months repeated storms maintained a surface layer of fresh snow in the study area. The assumption of 80 percent allowed for periods between storms when debris from trees darkened the snow surface to a slight degree, thus lowering the albedo.
As Table 6 suggests, solar radiation was an important heat source for snowmelt during February and
May. The theoretical snowmelt computations indicated that these months were represented by high radiation having sufficient calorific content to melt 25.13 inches
(unadjusted water equivalent) of snow during winter.
Storm occurrence and cloud cover was at a minimum during these months,and high values of radiation snowmelt were expected. However, this value was unrealistic even though solar radiation is usually the principal cause of snowmelt during an entire season. Without considering any other sources of heat, radiation alone was sufficient to account for 34.09 inches of water lost from the snow pack
(Table 6). However, forest cover, aspect, and slope Table 6. Theoretical solar radiation snowmelt on Horse Mountain as compared with observed snowmelt from all heat sources.
SOLAR RADIATION THEORETICAL MELT CORRECTED OBSERVED MELT IN INCHES IN LANGLEYS IN INCHES MELT IN INCHESd/ FROM ALL HEAT SOURCES (1) (2) Gross Actual Water Actual Actual snow decrease Net Month monthly Water snowc/ equiv. snow at snow depth marker monthly v.b/equi
Feb. 7,606.1 1,521.2 8.02 18.3 4.81 11.0 15.5
March 5,797.0 1,159.4 5.74 13.2 3.44 7.9 10.0 7 3 April 3,182.4 636.5 3.22 7.4 1.93 4.4 6.0
May 14,472.7 2,894.5 17.11 39.3 10.30 23.6 95.0
MEAN 7,764.6 1,552.9 8.52 19.6 5.12 11.7 31.6 a/Albedo of 80 percent assumed.
Columnb/Column 1 divided by mean monthly snow quality (Table 21, page 127) times 203 langleys required per inch of equivalent snowmelt at 100 percent snow quality. c/ Column 2 divided by mean density of snow profile (0.436) from Table 16, page 122.
Theoreticald/Theoretical values were reduced by 40 percent as discussed by Linsley et al. (1949). See page 74. 74
steepness undoubtedly decreased the amount of insolation
received in other portions of the study area, thereby
reducing snowmelt. Absorbed radiation may also have been
dissipated as latent heat of vaporization during periods
of sublimation. Thus, the problem of snowmelt computation from the theoretical viewpoint involved many complex
relations that could not be quantified in this study.
Other studies have indicated that theoretical snowmelt
computations overestimate actual melt by 35 to 45 percent
(Linsley et al., 1949). A correction factor of 40 percent
was accordingly applied in Table 6 (page 73) to give more
reasonable monthly snowmelt values. Even after adjust-
ments had been made, it was evident that solar radiation
was the major source of heat for snowmelt during all
months except May. Heat transfer by air convection was
probably the primary cause of snowmelt during May since
warm north winds evolved from the continued presence of
the Pacific High during this month. 75
Snow quality analysis
Results
A graph of snow quality from January through May provided insights on snow cover stability from a hydrologic and recreation standpoint (Figure 19). Snow is seldom capable of maintaining a quality of less than
95 percent without drainage, and during periods of rapid melting the quality is lowered to 85 percent or less
(Butler, 1957). Hence, the curve in Figure 19 illustrates that the snow cover was in a state of rapid deterioration during the first half of January, February, and all of
May, and as field observations indicated, high flows ensued from the headwaters of Ruby Creek during these months.
Low snow quality and insufficient snow cover during the first half of January and February provided no skiing, whereas high quality and deep snow cover in March and
April provided excellent skiing conditions. Low temper- atures in March and April undoubtedly maintained snow quality in excess of 95 percent during these months.
Snow cover during the first half of May was conducive to 76
Figure 19. Snow quality fluctuation on Horse Mountain during January through May 1967 (From Table 21, page 127). 77 skiing, but unfortunately the low quality (82 percent) produced a surface layer of slush that was approximately six inches in depth and which severely reduced the desirability and safety of skiing.
Double distance thermographs
Thermograph probes within the snow profile and at the soil surface level provided little basis for weekly correlation of snow temperature with quality since temper- atures at these levels varied only between 30 and 32 degrees throughout the season. A decrease in snow temperature with depth was expected since similar results were reported from the Central Sierra Snow Laboratory, where subsurface temperatures were four to eight degrees colder than snow surface temperatures when snow depth exceeded 70 inches (United States Department of Commerce,
1959). Mean seasonal snow quality was therefore similar at depths of one-third and two-thirds of the snow cover because of the absence of temperature gradation with depth increase. Respective means (January through May) for each depth were 93.9 and 93.8 percent (Table 21, page 127). 78
The insulating ability of snow was evident from thermograph tracings as the soil surface was never colder than 30 degrees throughout the measurement period. In addition, the soil was never frozen more than 0.50 inches in depth as observed when snow quality pits were dug during testing periods. Thus the ground was shielded from the sub-freezing air temperatures of March and April by a deep snow cover. In addition, the snow surface temperature was stabilized at 32 degrees during the season except when ambient temperatures fell below freezing, in which case the surface temperature approximated the temperature recorded in the weather station shelter.
Data were limited to establish this relationship as the snow surface probe was often covered by a layer of fresh snow and occasionally buried itself in the snow pack due to radiation warming.
Analysis of snow sampling results
Variation between study basins
The technique of comparing two groups of unequal sample size by Student's "t" test (Snedecor, 1956) was used to test for significant differences between the 79 average snow depth and water equivalent of the two basins
(Figure 20). Taking as the null hypothesis that study basin measurements were from the same population, tests were made comparing the basins on six different sampling dates (Table 7, page 81). A description of the formula used and a sample calculation are in Table 22 (page 128).
Comparisons between average snow depth and water equiv- alent of forest in basins indicated a variation that was similar when the total area of the developed basin was compared with the undeveloped basin. Therefore, only the latter statistical comparison was made in this study since it provided more degrees of freedom with greater possibil- ity for detection of significant differences between compared areas.
Of the six comparisons, the first three snow depth means were significantly different at the five percent level of acceptance. Thus, from February 18th to
April 2nd the probability was 95 percent that the deeper snow cover found in the undeveloped basin was attributed to a population difference caused by an interaction of physiographic factors within the undeveloped basin itself, with only a five percent chance that obtained results were 80
MEAN SNOW DEPTH IN UNDEVELOPED BASIN
MEAN SNOW DEPTH IN DEVELOPED BASIN
MEAN WATER EQUIVALENT IN UNDEVELOPED BASIN
MEAN WATER EQUIVALENT IN DEVELOPED BASIN
Figure 20. Snow depth and water content fluctuation in both study basins on Horse Mountain during January through May 1967 (From Table 23, page 129). 81
Table 7. Comparison of snow depth and water content between the developed and undeveloped study basins using Student's "t" test.
COMPARISON OF SNOW COMPARISON OF WATER DEPTH IN INCHES EQUIVALENT IN INCHES
Sampling t value t value date
2.45 2/18/67 2.04
3/ 4/67 2.382.452.43
4/ 2/67 1.65
4/30/67 0.36 0.59
5/14/67 0.23 0.41
5/21/67 1.38 1.18
a/ — t values significant at the 5 percent level for 43 degrees of freedom. 82
due to random variation from a single population mean.
Similar significant results were obtained with comparisons
of average water equivalent on February 18th and March
4th. From March 2nd to May 21st comparisons of average
snow depth and water equivalent between basins were not
significantly different. In spite of the sample size
limitation as discussed on page 86, the author is con-
vinced by field observations that an increase in melt rate
in the undeveloped basin was induced by northward migra-
tion of the sun after the spring equinox (March 21st) and
accounted for non-significant comparisons after April 2nd.
Variation within basin
Comparisons also were made between the average
snow depth and water equivalent on ski slopes and in the
adjacent forest of the developed basin (Table 24, page
130). Again taking the null hypothesis that the means
came from the same population, tests were made to compare
slopes and adjacent forest on seven sampling dates
(Table 8). A description of the formula used to compare
means from equal sample sizes is in Table 22 (page 128).
Of the seven comparisons, only two of the group
means for water equivalent were significantly different 83
Table 8. Comparison of snow depth and water content between ski slopes and forest adjacent to the slopes in the developed basin using Student's "t" test.
COMPARISON OF SNOW COMPARISON OF WATER DEPTH IN INCHES EQUIVALENT IN INCHES
Pooled Sampling Pooled standard t value standard date t value deviation deviation
1/ 7/67 1.02 3.74 0.73 1.50 1.81 2.52 2/18/67 4.83 2.06 2.21 3/ 4/67 1.35 6.07 2.24
4/ 2/67 0.39 9.20 1.45 3.59
4/30/67 0.03 8.65 1.60 3.94
5/14/67 0.96 10.50 1.53 4.66
5/21/67 0.55 8.06 1.58 3.13
MEAN 7.29 3.02
a/— t values significant at the 5 percent level for 28 degrees of freedom.
t value significantb/ at the 10 percent level for 28 degrees of freedom. 84 at the five percent level of acceptance. Snow depth comparisons were non-significant on all dates except on
February 18th when results were significant only at the
10 percent level. Compaction of snow on slopes by skiers reduced the difference between sample means when respec- tive water equivalents were significant on February 18th and March 4th, thereby yielding non-significant depth comparisons at the five percent level on these dates.
In summation, the results in Table 8 (page 83) suggest that early season accumulation was significantly higher on the slopes than in the forest, and that differences in late season accumulation and retention were non- significant between the slopes and adjacent forest.
However, theoretical sample size findings as discussed in the following section reveal that a much larger sample size would be needed to detect the presence of significant differences during late season accumulation and retention.
Theoretical sample size determination
The utilized sample size of 30 points in the developed basin provided a reliable estimate of mean snow depth and water content as desired by the Humboldt Ski
Club. The following formula devised by Snedecor (1956) 85
permits computation of a theoretical sample size based
upon the pooled sample standard deviation obtained from
measurement data:
where: = the population difference (10 percent in
this study).
s = the mean pooled standard deviation (7.29
inches from Table 8, page 83).
t = t table value where degrees of freedom
equals n-1, i.e. 30-1 = 29.
n = theoretical sample size.
Applying the 90 percent level of confidence, the
sample size is computed as follows, where is 10 percent
(0.10 x 28.2 = 2.82 inches) of the mean snow depth from
the six sampling dates in Table 24 (page 130):
n = 19.3
This calculation provides a new estimate of the t
table value for 10 percent (1.729) and must therefore be 86 repeated. The new calculation yields a sample size of
19.9 measuring points and does not change the t table value at the 10 percent level. Therefore, in the devel- oped basin, a sample size of 20 points would be needed to provide an estimate of snow depth within 10 percent at a confidence level of 90 percent if the variability is not significantly different from that experienced in this study. Using the same formula, a sample size of 24 would be needed to provide equivalent reliability if an estimate of water content is desired.
Although the chosen sample size provided a reliable estimate of average snow depth and water content in the developed basin, the sample was too small to permit detection of significant differences between sample means on most dates because of large variability among measure- ments. Comparisons on certain dates yielded significant results only because of large differences between sample means. A slight modification of the above formula facilitates computation of a theoretical sample size based upon measurement variability when differences between sample means are to be tested as was done in this study
(Snedecor, 1956): 87
where: = the smallest population mean difference
desired (10 percent in this study).
s = the mean pooled standard deviation (7.29
inches from Table 8, page 83).
t = t table value where degrees of freedom
equals 2(n-1), i.e. 2(15-1) = 28.
n = theoretical sample size.
Using the 90 percent level of confidence, the theoretical sample size needed to detect significant differences in snow depth between slopes and adjacent forest is computed as before while incorporating the above modification:
n = 38.8
This calculation provides a new estimate of the t table value for 10 percent (1.686) and must therefore 88 be repeated. The new calculation yields a sample size of 37.9 measuring points. Therefore,to be 90 percent confident that significant differences between sample means will be detected on all dates, a sample size of
38 in each type of compared terrain would be needed.
Using the same formula, a sample size of 46 would be needed to detect significant differences between slopes and forest for water content. Thus, the sample size used in this study would have to be tripled to assure statis- tical reliability for comparative purposes on all sampling dates.
Snowfall accumulation and retention in basins as related to physiographic parameters
Elevation
A map depicting the average snow depth in study basins from February 18th to May 21st was constructed by connecting average snow measurements from each sampling point during the above period. As was expected, isolines of average snow depth gradually increased as elevation increased, with the trend most obvious in the undeveloped basin (Figure 21). Snow depth increased in this basin from 20 inches at an elevation of 4,200 feet to 50 inches 89
Figure 21. Mean snow depth in developed and undeveloped basins from February 18th to May 21st 1967 (Isolines of snow depth extrapolated from data in Table 25, page 131). 90 at 4,800 feet in elevation. Use of these extremes yielded an average snow accumulation increase of five inches per
100 feet elevation rise.
In the developed basin snow depth generally increased from 20 inches at an elevation of 4,300 feet to 40 inches at 4,800 feet. Therefore, snow accumulation increased four inches per 100 feet elevation increase in the basin. Figure 21 (page 89) further indicates that isolines in the developed basin generally were located
100 feet higher in elevation than in the undeveloped basin. For comparative purposes, mention should be made that an average snow accumulation of two inches per 100 feet elevation increase was tabulated at the Central
Sierra Snow Laboratory on slopes of all aspects for elevations in excess of 7,000 feet (Anderson, 1957).
Snow hydrologists in Colorado report that slope steepness is much more important in determining the rate
of snow disappearance on slopes of all aspects than is
elevation (Garstka, 1958). On Horse Mountain the opposite appeared true since elevation significantly influenced
snow accumulation by adiabatic cooling during storms.
Persistence of snow in spring was therefore a function of 91 elevation except for localized areas where other physio- graphic features affected accumulation and retention as is discussed in the following sections. Measurements from an additional weather station located at the 4,300 foot elevation level would be needed to confirm this hypothesis.
Exposure
Certain portions of both study basins were less effective in retaining snowfall because of extreme exposure to wind and solar radiation. For example, from
February 18th to May 21st the average snow depth near the summit of the undeveloped basin was only 30 inches as compared to 50 inches at an elevation difference of 100 feet below the summit (Figure 21, page 89). Summit slopes were constantly buffeted by north winds as well as south wind eddy currents and were adversely exposed to solar radiation. Slopes near the summit of the developed basin were less affected than those in the undeveloped basin since the basin is oriented more directly to due north, thereby reducing slope exposure to solar radiation.
At lower elevations, exposure of the spur ridge between the study basins to wind and radiation rendered this area 92
less effective in retaining snow cover, as the isoline
of 20 inches in Figure 21 (page 89) suggests. In the
center of the developed basin a pocket of deeper snow
(40 inches) was related to retention caused by extreme
basin concavity that channeled cold air drainage into
this area from slopes above. On most sampling dates a
surface ice crust was observed throughout the day in
this area while melting went on in other areas.
Anemometers would be most useful in evaluating the
exposure of the spur ridge and the summit of the undevel-
oped basin to wind. The snow simply may have been blown
out of these areas by strong north winds. Thus, the
presence of deeper snow in the center of the developed
basin while snow was less deep elsewhere may have been
caused by an interaction of wind-induced snow accumulation
and cold air drainage, with greater accumulation and
prolonged retention of snow in this area.
Aspect
Opposing aspects in the developed basin were
compared using Student's "t" test, with comparisons made
of aspects that were oriented north, 40 degrees east,
and north, 44 degrees west. Average snow depth 93 measurements from sample points four, six, and fifteen were compared with measurements from points two, three, and five. This was made possible since an analysis of
Table 9 (page 112) showed that discrepancies in average elevation, slope steepness and crown canopy between these compared samples were negligible, thereby attributing snow cover variation solely to aspect orientation.
Comparisons were made for the same dates recorded in
Table 8 (page 83) when it was observed that average depths were two to five inches deeper on the northwest slopes.
However, variability was high among measurements and significant differences (90 percent level) were found only on February 18th, when a t value of 2.20 was computed using four degrees of freedom. Measurement variability was scrutinized further for determination of theoretical sample size. Applying the method mentioned earlier, a sample size of 53 points per aspect would be needed to provide detection of significant differences in snow depth between these aspects on all dates at the 90 percent confidence level. 94
Slope steepness
Slopes in the developed basin were compared using the "t" test on the same dates mentioned above to determine the effect of steepness on snow retention.
The intermediate slope was compared with the easternmost ski slope by testing average snow depth measurements from sample points eight, nine and ten against sample points one, two and three. The same method was employed as when aspects were compared, with points chosen for each sample with elevation, aspect and crown canopy similar so that snow cover variation was attributed solely to slope steepness. The intermediate slope averages 23 percent, the other slope 48 percent.
On all dates when comparisons were made, the average depth on the steeper slope ranged from five to ten inches higher than the average depth on the intermediate slope. Significant differences at the five percent level were detected on February 18th, March 4th and April 2nd.
From this it can be concluded that the steeper slope was significantly more effective in inhibiting snow melt during the 43 day period, assuming that the intermediate 95 slope was not wind swept more than the steeper slope.
Considering sample variability, a theoretical sample size of 16 points per slope would be needed to detect signifi- cant differences in snow depth between these slopes on all dates at the 90 percent confidence level.
Crown canopy
Sample points having a high percentage of crown coverage were not statistically compared with points having low crown coverage since cases did not exist where the influence of other variables, such as slope and elevation could be eliminated. It was observed however, from sample point measurements in the developed basin where crown coverage exceeded 75 percent, that snow depth prior to the arrival of storms in March and April was only
50 to 60 percent of the average basin depth. Differences at these points were only slight during March and April as storms were of long duration and interception losses were low in proportion to the total precipitation of major storms. Further investigation would be necessary to establish that high interception losses will occur and reduce snow cover accumulation when early season storms are of short duration and when crown coverage exceeds 75 96 percent, as it does at sample points 27, 28, and 29 in the developed basin.
Generally, snow will melt slower in forested areas than in large clearings because of shading of the forest and the higher windspeeds in the open that increase melt through convection and condensation (Reifsnyder, 1965).
During May however, in the developed basin snow melted first from around large trees before disappearing on the slopes. The logical explanation for this is that crown canopies absorbed most of the short-wave solar radiation and transferred the heat to tree boles by stem conduction from which re-radiation occurred in the form of long heat waves, thus melting snow in a circular pattern from around the larger trees. Compaction of snow by skiers may have caused snow to persist longer on the steeper slopes in the developed basin than in the adjacent forest by binding the snow crystals. It is important to mention however, that measurement differences of average snow depth between the forest and slopes were not large enough to extend the length of skiing period on the slopes during the spring thaw. 97
Recreation use during 1966-1967 winter
The total number of skiers and snowplayers were recorded on weekends by ocular counts made early in the afternoon. On days when the author was not in the field the information was compiled by a member of the ski club employing the same method. A total of 2,380 skier days
(Table 26, page 133) were recorded during the study period as compared to 2,200 reported to the Forest Service by the ski club. The discrepancy reflects the number of skiers who did not purchase rope tow tickets. A count of 680 snowplayers agreed closely with the Forest Service report of 700.
Average use for each day of the weekend throughout the study period was 70 skiers. Approximately 150 skiers were recorded on each day of the weekend during April 8th and 9th when competitive slalom races were held. Approxi- mately 200 skiers represents the maximum use capacity on the intermediate slope above the ski lodge. Another 200 skiers safely could be accommodated on the steeper slopes in the developed basin. The maximum capacity of the total ski area would therefore be approximately 400 skiers, 98 assuming that half of these skiers were qualified to use the steeper slopes.
Recreation potential exceeded demand during all months (Figure 22). During March and April the snow cover was suitable for skiing on all but three days.
Nevertheless, the slopes were used only 12 days in March and eight in April. Use was restricted by the operation of ski tows on weekends only, except at Easter when tows were operated from March 20th to March 25th. It is doubtful that weekday operation of facilities (other than on holidays) would entice a significant number of skiers to the area since high school and college recre- ationists as well as most regular workers would be excluded. Students constituted the major portion of users of the ski area during the study period.
Skiing conditions were optimum during March and
April as indicated by the number of skiers represented in Figure 22. During these two months alone, 1,400 skiers, or 59 percent of the season total were counted on the slopes. The number of snowplayers during all months (except December) was less than one-half the number of skiers. Thus the majority of recreationists traveled to the area primarily to ski. 99 use during the winter of 1966-1967 (From Table 26, page 133). use during the winter Figure 22. Relationship of skiing potential on Horse Mountain to actual of skiing potential on Horse Mountain Figure 22. Relationship 100
Inclement weather had little effect on use since weather was favorable on all but a few weekends through- out the study period. During storm periods skiers were confined to the intermediate slope because of poor visibility on the steeper slopes. Horse Mountain skiers are a hardy and dedicated lot, as evidenced by surprising turnouts on the slopes during blustery and frigid days.
Observations during field work
In several locations, indicators of erosion were observed where material disturbance of protective vege- tative cover had occurred from slope clearing activities during the summer of 1966. The most critical area was located along the headwaters of Ruby Creek where stream diversions created an erosion pavement along the pathway of the 1,500 foot rope tow. Removal of surface soil and exposure of dark colored bedrock severely reduced the snow holding potential of this area and precluded the use of the rope tow during certain periods when snow cover on the slopes was sufficient for skiing. However, late season restoration of the stream to its original 101 channel by cross-ditching alleviated the melt problem along the tow.
An additional observation indicated that the bottom of the intermediate slope had been used as a landing to stockpile logs during slope clearing. Ensuing site disturbance resulted in exposure of the dark colored
soil and reduced the snow holding capability of this area throughout the entire season. Seeding of the disturbed
site to grass was effected and will hopefully solve this
problem.
Problems encountered during field work
Comments in this section are included for the
benefit of future aspirants to high elevation snow
hydrology projects. It is anticipated that mention of
major inconveniences experienced by the author will be
useful.
Attempts to use the snow sampler were futile (even
if well waxed) when the air temperature was below freezing, as the extracted snow core froze to the inside
of the aluminum tubing. On a few occasions this problem 102 prevented the sampling of all 45 points in one day. Snow sampling is therefore not recommended at temperatures below freezing.
The door to the weather station shelter was found frozen closed when maintenance was required during severe storms. An anti-defrostant aerosol can was effective in solving this problem.
In December, the presence of an ice crust on slopes in both study basins necessitated the use of mountain- eering crampons to assure travel safety between sample points. The use of snowshoes proved very effective in traveling to the weather station, but were most cumbersome when used on the slopes during warm periods with rapid melting. CONCLUSIONS
This study provides the first major compilation and analysis of factual snow hydrology data for higher elevations in Humboldt County. The results of this study indicate that snowfall is more important to the hydrology of higher elevations in this region than has previously been mentioned by other authors. Of major hydrologic significance is the finding that April snow water storage on slopes during the study period was 19.2 inches (Table
23, page 129) or 27 percent of the total annual precipi- tation of 70 inches. Low temperatures in April with high snow retention produced an atypical snow cover during the spring thaw in 1967.
Presence of a measurable snow cover on all slopes prior to the winter solstice and well beyond March 21st strongly suggests that Horse Mountain and other areas of similar elevation in Humboldt County are eligible for inclusion within the California Snow Zone boundary.
Considering the variability experienced in this study, a sample size of 24 points would be needed to provide an estimate of average snow depth and water 104 content in basins within 10 percent at a confidence level of 90 percent. In future studies where the measurement and acreage variation is not significantly different from that found and tested in this study, and where the same confidence level is acceptable, a sample size of 46 would be required for testing of measurements comparing
ski slopes and adjacent forest.
Elevation, exposure, and slope steepness are major
physiographic variables affecting snowfall accumulation and retention on north slopes of Horse Mountain. A
significantly larger sample size is needed to substantiate the effect of crown canopy on snowfall accumulation, although crown cover in excess of 75 percent appears to
be highly detrimental. Northwest aspects appear to retain
snow better than northeast aspects, but comparisons have
not proven statistically significant for most dates.
Precipitation during the study period was 18
percent below normal primarily because of dry periods
during February. Nevertheless, extremely low temperatures
in April prolonged snow retention and extended the skiing
season a few weeks longer than normal. A comparison of
climatic information with recreation use data strongly 105 suggests that the demand for winter snow sports in
Humboldt County is not solely regulated by snow con- ditions. For this reason, current management decisions pertaining to the Horse Mountain Ski Area should focus on the improvement of present facilities only, pending a more intensive investigation of demand relationships before substantial monetary investments for further expan- sion are warranted. Completion of the freeway on Highway
299 east from Blue Lake in the near future will probably alter current demand trends by improving access to the area. Future demand may warrant facility expansion to the undeveloped basin, and if so, the author strongly recom- mends that only the east side (northwest aspect) be used for ski slopes because of poor snow retention on the west side.
Continued collection of snowfall information for
Horse Mountain is strongly urged to provide conclusive long-term data. The inclusion of anemometers is recom- mended to provide insights on snowmelt and snow drifting as influenced by wind in this area. Furthermore, the installation of a recording stream gage below both study basins would permit hydrologic calibration of the basins 106 through the integrated use of established snow sampling points and the weather station site. LITERATURE CITED
Anderson, H.W., and T.H. Pagenhart. 1957. Snow on forest slopes. Proceedings Western Snow Conference, Colorado State University. Fort Collins, Colorado. 106p.
Anderson, H.W. 1963. Managing California's snow zone lands for water. Pac. S.W. For. and Rng. Exp. Sta. Berkeley, California. 28p.
Belfort Instrument Company. 1965. Instruction book for pyrheliograph catalog no. 53850. Book no. 11900. Baltimore, Maryland. 8p.
Bernard, M., and W.T. Wilson. 1941. A new technique for the determination of the heat necessary to melt snow. Trans. Am. Geophys. Union. 22: 178-181.
Black, P.E. 1964. A guide to the Soil-Vegetation Maps of Humboldt County, California. Div. of Nat. Res., Humboldt State College. Arcata, California. 16p.
Butler, S.S. 1957. Engineering Hydrology. Prentice- Hall, Inc. Englewood Cliffs, New Jersey. 356p.
Byram, G.M., and G.M. Jemison. 1943. Solar radiation and forest fuel moisture. Jour. Agr. Res. 67: 149-176.
California Department of Water Resources. 1965. Snow survey measurements through 1964. Bulletin no. 129. Sacramento, California. 366p.
. 1967. Water conditions in California. Bulletins 120-66-67. Sacramento, California. 30p.
. 1968. Hydrologic data-North Coastal Area. Bulletins 130-63-67. Volume 1. Sacramento, California. 100p. 108
California Division of Mines and Geology. 1966. Geology of Northernalifornia. Bulletin no. 190. San Francisco, California.C 508p.
California Public Outdoor Recreation Plan Committee. 1960. California public outdoor recreation plan. Part II. Sacramento, California. 204p.
Cotton, C.A. 1958. Geomorphology. Whitcombe and Tombs Limited. London. 505p.
Garstka, W.U., L.D. Love, and F.A. Bertle. 1958. Factors affecting snowmelt and streamflow. Cooperative snow investigations, Fraser Experimental Forest. Fraser, Colorado. 189p.
Humboldt Ski Club. 1968. Unpublished scrapbook of newspaper articles of club activities from 1946 to 1968. Eureka, California. 40p.
Ingersoll, L.R., J.M. Miles, and T.A. Rouse. 1953. A laboratory manual of experiments in physics. McGraw- Hill Book Co., Inc. New York. 286p.
Jenkins, O.P. 1962. Geologic map of California-Redding sheet. California Division of Mines and Geology. San Francisco, California. 1p.
Linsley, R.K., M.A. Kohler, and J.H. Paulhus. 1949. Applied hydrology. McGraw-Hill Book Co., Inc. New York. 689p.
McAuliffe, J.P. 1929. Snow and sleet at unusually high temperatures. Monthly Weather Review, no. 57. 1p.
Meyer, H.A., and D.P. Worley. 1955. Measurements of crown diameter and crown cover and their accuracy for 1:12,000 photographs. Photogram. Engineer. 21: 372-375.
Reifsnyder, W.E., and H.W. Lull. 1965. Radiant energy in relation to forests. United States Forest Service Tech. Bul. no. 1344. Washington, D.C. 111p. 109
Rikhter, G.D. 1954. Snow cover, its formation and properties. United States Army Corps of Engineers. Snow, Ice and Permafrost Establishment. Wilmette, Illinois. 15p.
San Francisco Examiner. February 8, 1953. Vol. CLXXXXVIII, no. 39. San Francisco, California. 172p.
Snedecor, G.M. 1956. Statistical methods. Iowa State University Press. Ames, Iowa. 534p.
Southern Pacific Railroad Company. 1965. The Christmas week storm disaster on the Southern Pacific and Northwestern Pacific. 23p.
The Humboldt Times. January 30, 1947. Vol. CLXVII, no. 26. Eureka, California. 8p.
Trewartha, G.T. 1954. An introduction to climate. McGraw-Hill Book Company, Inc. New York. 402p.
United States Army Corps of Engineers. 1965. Report on floods of December 1964 in Northern California coastal streams. San Francisco District Corps of Engineers. Volume 1. 80p.
United States Department of Commerce. 1959. Snow hydrology. Summary report of snow investigations. Washington, D.C. 437p.
. 1949-1967. Climatological data in California. Environmental Science Services Admin- istration. Ashville, N.C.
United States Forest Service. 1947-1966. Annual statistical reports on recreation visits from 1947 to 1967 in the Lower Trinity Ranger District, Six Rivers National Forest. Eureka, California.
. 1962-1967. Recreation use information reports for the Horse Mountain Winter Sports Area from 1962 to 1967. Six Rivers National Forest Headquarters. Eureka, California. 110
United States Geological Survey. 1964. Compilation of surface water supply records of the Pacific Slope Basins in California. Water supply paper no. 1735. Washington, D.C. 715p.
United States Weather Bureau. 1964. The climate of Humboldt and Del Norte Counties. Humboldt and Del Norte Counties Agric. Exten. Service. Eureka, California. 34p.
Wisler, C.O., and E.F. Brater. 1965. Hydrology. John Wiley and Sons, Inc. New York. 408p.
Zinke, P.J. 1965. Influence of land use on floods in relation to run-off and peak flows. Proceedings from the California State Board of Forestry Meeting, 1965. Sacramento, California. 6p. APPENDIX Table 9. Physiographic parameters measured at each snow sampling point in the study area.
Sample Compass bearing Horizontal Elevation Slope Percent point to point distance in feet Aspect percent crown number in feet canopyb DEVELOPED BASIN - Ski slopes 1 N. 75° E. 24 4,780 N. 65° W. 45 20 2 S. 34° W. 39 4,500 N. 57° W. 49 15 3 S. 40° W. 55 4,350 N. 52° W. 50 15 4 S. 85° W. 47 4,330 N. 48° E. 52 20 5 N. 72° W. 26 4,580 N. 24° W. 42 25 6 N. 35° W. 43 4,590 N. 32° E. 43 10 ZI1 7 S. 50° E. 45 4,770 N. 36° E. 40 15 8 N. 82° E. 70 4,740 N. 38° W. 26 0 9 S. 30° W. 65 4,680 N. 68° W. 22 5 10 S. 9° W. 62 4,720 N. 39° W. 20 0 11 N. 46° E. 25 4,750 N. 29° E. 41 15 12 S. 1° W. 53 4,660 N. 15° W. 22 0 13 N. 70° E. 32 4,530 N. 36° E. 27 10 14 N. 26° W. 35 4,450 N. 81° E. 50 20 15 S. 66° E. 40 4,600 N. 40° E. 43 20 N. 45° W. AVERAGES 4,602 N. 43° E. 38 13 Refers to measurement from tagged tree to snow sample point. bWithin a 75-foot radius circle (2/5 acre) from snow sample point. Table 9. (continued)
Sample Horizontal Percent point Compass bearing distance, Elevation Aspect Slope crown number to pointa/ in feeta/ in feet percent canopyb/ DEVELOPED BASIN - Forest adjacent to slopes
16 N. 20° E. 20 4,790 N. 37° W. 47 60 17 N. 68° E. 31 4,750 N. 65° W. 55 45 18 S. 31° W. 18 4,630 N. 55° W. 54 50 19 N. 69° W. 20 4,430 N. 35° W. 46 70
20 N. 83° W. 15 4,400 N. 52° W. 58 55 1 1 21 S. 70° W. 20 4,440 N. 56° E. 52 65 3 22 S. 42° E. 22 4,670 N. 59° E. 40 70 23 N. 78° E. 13 4,750 N. 18° W. 37 55 24 N. 55° W. 20 4,860 N. 15° W. 48 70 25 S. 10° E. 17 4,800 N. 57° E. 45 75 26 S. 13° E. 20 4,840 N. 75° W. 26 45 27 N. 72° W. 19 4,780 N. 70° W. 24 80 28 N. 8° W. 28 4,620 N. 4° E. 24 90 29 N. 4° E. 11 4,540 N. 61° E. 45 85 30 S. 46° E. 13 4,680 N. 51° E. 42 50 N. 47° W. AVERAGES 4,665 N. 48° E. 43 64 Refers to measurement from tagged tree to snow sample point. b Within a 75-foot radius circle (2/5 acre) from snow sample point. Table 9. (continued)
Sample Horizontal Percent Elevation Slope point Compass bearing to point distance Aspect crown number in feeta/ in feet percent canopy /
UNDEVELOPED BASIN
31 N. 49° W. 25 4,900 N. 24° E. 10 40 32 S. 65° E. 39 4,790 N. 22° W. 50 65 33 N. 60° E. 16 4,760 N. 3° W. 40 75 34 S. 17° E. 14 4,790 N. 7° E. 38 40 35 S. 19° W. 21 4,740 N. 19° W. 37 50 11 4 36 S. 72° E. 34 4,650 N. 20° W. 40 60 37 N. 76° W. 17 4,690 N. 57° E. 46 45 38 N. 70° E. 23 4,450 N. 85° E. 50 40 39 N. 3° E. 21 4,340 N. 75° E. 47 50 40 N. 60° W. 54 4,200 N. 35° E. 45 35 41 S. 41° W. 17 4,390 N. 32° W. 42 80 42 N. 9° E. 20 4,260 N. 40° W. 56 50 43 S. 10° E. 22 4,400 N. 35° W. 50 50 44 N. 20° E. 23 4,440 N. 11° W. 42 60 45 N. 51° E. 19 4,550 N. 13° W. 40 85 N. 473822°° W. AVERAGES 4,557 N. E. 42 55 ° W. TABLE AVERAGES 4,608 N. 46° E 41 44 a/Refers to measurement from tagged tree to snow sample point. Within a 75-foot radius circle (2/5 acre) from snow sample point. 115
Table 10. Scientific and common names of all conifers and common shrubs found in the Horse Mountain Ski Area.
Scientific name Common name
Conifers:
Abies concolor white fir
Chamaecyparis lawsoniana port-orford-cedar
Libocedrus decurrens incense-cedar
Pinus jeffreyi Jeffrey pine
Pinus lambertiana sugar pine
Pinus monticola western white pine
Pinus ponderosa ponderosa pine
Pseudotsuga menziesii Douglas-fir
Thuja plicata western redcedar
Shrubs:
Amelanchier pallida service-berry
Arctostaphylos patula greenleaf manzanita
Arctostaphylos viscida whiteleaf manzanita
Castanopsis chrysophylla giant chinquapin
Ceanothus cuneatus buck brush
Ceanothus integerrimus deer brush
Quercus vaccinifolia huckleberry oak
Rhododendron occidentale western azalea Table 11. Depth and water content of snow at Big Flat in Trinity County (elevation 5,100 feet) from 1946 to 1967 (From Calif. Dept. of Water Resources, 1965-1967).
DEPTH AND WATER CONTENT IN INCHES February March April May Year Date Depth W.C. Date Depth W.C. Date Depth W.C. Date Depth W.C. 1946 1-29 55.0 18.7 2-26 64.1 23.9 3-25 52.9 23.6 -- -- 1947 2-1 14.1 2.4 3-1 6.0 1.9 3-28 6.2 2.1 ------1948 2-3 10.0 3.5 3-1 7.5 3.4 3-26 21.6 7.7 -- -- 1949 2-1 33.7 9.2 2-28 38.8 15.4 3-27 51.9 23.6 5- 4 0.0 0.0 1950 2-1 35.9 10.2 2-27 32.0 13.5 3-27 42.4 15.7 4-30 0.0 0.0
1951 1-30 31.9 9.6 3-6 40.9 14.7 3-27 21.9 9.7 5- 6 0.0 0.0 11
1952 1-31 74.1 28.7 2-26 72.2 31.0 3-24 93.5 35.7 4-30 23.6 12.0 6
1953 2-1 45.1 19.0 3-1 37.7 19.6 4-4 37.5 18.3 4-29 16.8 8.4 1954 2-1 57.5 17.7 3- 3 49.0 22.0 3-29 49.2 22.9 -- -- 1955 1-30 36.1 10.3 2-28 40.1 11.1 4-1 17.1 5.1 5- 2 8.7 2.8 1956 2-1 58.4 20.0 3-1 87.7 30.4 3-25 63.7 27.1 4-30 18.5 9.5 1957 1-31 28.0 9.2 2-28 10.6 4.9 3-27 8.2 2.9 5-3 2.0 0.4 1958 2- 2 51.6 14.6 3- 3 47.1 19.5 4- 2 89.2 24.2 4-30 31.7 15.1 1959 1-29 27.1 9.1 2-27 56.2 20.1 4-5 23.8 9.7 4-27 0.0 0.0 1960 2- 3 33.0 8.7 3-1 40.2 14.6 4-5 27.8 16.9 5-2 0.0 0.0 1961 2-1 13.6 6.4 3-2 13.5 4.8 4-4 19.5 8.9 5-3 0.0 0.0 1962 1-31 27.7 8.0 3-1 96.0 17.7 4-1 49.3 19.9 5-1 0.0 0.0 1963 1-28 0.0 0.0 2-26 0.0 0.0 4- 4 16.4 5.4 4-29 10.7 4.6 1964 1-30 41.2 14.8 2-26 32.9 12.6 3-30 29.8 12.1 4-30 0.0 0.0 1965 1-28 32.6 12.3 2-25 24.6 11.2 4- 4 6.3 3.4 4-27 0.0 0.0 1966 1-28 45.7 17.0 3- 3 69.2 23.6 3-25 57.8 23.4 4-29 7.8 4.8 1967 1-31 49.2 16.2 2-27 35.4 11.6 4- 4 37.4 16.3 4-28 45.8 22.5 MEAN 36.4 12.1 41.0 15.0 37.4 15.2 9.2 4.5 117
Table 12. Known and estimated snow depths for the Horse Mountain general area from 1946 to 1967.
a/Estimates by Dr. Walsh unless noted otherwise.
From Humboldt Ski Club scrapbook of newspaper clippings (1968).
Measured at weather station. Represents maximum depth during 1966-1967 season. 118
Table 13. Horse Mountain snow survey data sheet.
Weight of Mt. Rose snow sampler and extracted snow core within the tube. b/ Weight of empty sampler. Is dependent upon the number of lengths of tubing used.
/Water equivalent in inches. Column 2 minus column 3. Scale reading in ounces is equivalent to inches of water in the sampled snow cover.
/Column 4 divided by column 1, then multiplied by 100. Table 14. Monthly rainfall and snowfall on Horse Mountain during the winter of 1966-1967.
RAINFALL RAINFALL SNOWFALL AND SNOWFALL Total in Percentseason totalof Water equiv. Total in inches Percent of Total in Month inches (inches) season total inches
October 0.30 1.0 0.00 0.0 0.0 0.30 November 10.74 36.4 1.65 9.7 4.8 12.39 December 10.55 35.9 3.75 22.0 10.9 14.30 119
January 4.05 13.8 10.25 60.4 30.0 14.30 February 0.00 0.0 0.97 5.7 2.8 0.97 March 3.20 10.9 7.59 44.6 22.0 10.79
April 0.02 0.1 7.90 46.4 23.0 7.92 May 0.39 1.3 2.22 13.1 6.5 2.61 June 0.18 0.6 0.00 0.0 0.0 0.18
TOTAL 29.43 100.0 34.33 201.9 100.0 63.76
Computed by dividing monthly water equivalent by average density of freshly- fallen snow (0.17) on Horse Mountain.
Period from October 22nd to October 31st.
Period from June 1st to June 4th. Table 15. Analysis of individual storms on Horse Mountain during the winter of
1966-1967.
GENERAL DESCRIPTION RAINFALL SNOWFALL Dates Storm Duration Total in Percent of Water equiv. Amount in Percent of Month number in days inches storm total in inches inches storm total of storm
Oct. 1 22-23 2 0.30 100.0 0.00 0.0 0.0
Nov. 2 5- 7 3 0.96 76.0 0.30 1.8 24.0 3 11-15 5 3.13 100.0 0.00 0.0 0.0 12 0 4 17-23 6 5.35 97.3 0.15 0.9 2.7 5 27-29 3 1.30 52.0 1.20 7.1 48.0
Dec. 6 1- 9 9 8.65 71.5 3.45 20.2 28.5 7 11-13 3 1.20 100.0 0.00 0.0 0.0 8 20-20 1 0.10 100.0 0.00 0.0 0.0 9 29-30 2 0.60 66.7 0.30 1.8 33.3
Jan. 10 4- 5 2 0.00 0.0 0.40 2.4 100.0 11 19-31 13 4.05 29.1 9.85 58.0 70.9
Feb. 12 13-15 3 0.00 0.0 0.87 5.1 100.0 13 24-25 2 0.00 0.10 0.6 100.0
A minimum allowance of 24 hours of non-recorded precipitation was used to segregate storms, with a. storm defined as any period yielding measurable precipitation. Water equivalent per storm divided by average density of freshly-fallen snow (0.17). Table 15. (continued)
GENERAL DESCRIPTION RAINFALL SNOWFALL ofDates storm Total in Percent of Month Storm Duration Water equiv. Amount in Percent of number in days inches storm total in inches inches storm total
March 14 9-20 12 2.80 37.1 4.74 27.7 62.9 15 22-23 2 0.40 36.4 0.70 4.1 63.6 16 26-31 6 0.00 0.0 2.60 15.3 100.0
1 0.30 April 17 3- 3 0.00 0.0 1.8 100.0 12 18 5- 7 3 0.02 1.6 1.25 7.4 98.4 1 19 9-10 2 0.00 0.0 0.40 2.4 100.0 20 13-29 17 0.00 0.0 5.50 32.3 100.0
May 21 9-12 4 0.00 0.0 2.22 13.0 100.0 22 28-28 1 0.30 100.0 0.00 0.0 0.0 23 30-30 1 0.09 100.0 0.00 0.0 0.0
June 24 1- 1 1 0.18 100.0 0.00 0.0 0.0
TOTAL 104 29.43 34.33 201.9 AVERAGE PER STORM 4 1.22 1.43 8.4
A minimum allowance of 24 hours of non-recorded precipitation was used to segregate storms, with a storm defined as any period yielding measurable precipitation.
Water equivalent per storm divided by average density of freshly-fallen snow (0.17). 122
Table 16. Weekly snow measurements from the Horse Mountain weather station during the winter of 1966-1967.
Depth in Water equiv. Density in Date inches in inches percent
November 6 2.0 -- -- 12 0.0 -- -- 20 1.0 -- -- 28 8.0 4.0 50.0 December 3 13.0 6.0 46.1 10 20.0 9.0 45.0 18 13.5 7.0 51.8 22 12.0 6.0 50.0 31 13.0 7.0 53.8 January 7 17.0 11.5 67.6 14 12.0 5.5 45.8 21 21.0 6.5 30.9 26 31.0 11.5 37.2 29 22.0 9.5 43.2 February 4 24.0 9.5 39.6 12 16.0 8.0 50.0 18 22.0 10.5 47.8 26 22.0 9.5 43.2 March 4 20.0 9.5 47.5 11 42.0 10.5 25.0 19 36.0 14.0 38.9 27 33.5 14.5 43.3 April 2 57.0 19.0 33.4 9 55.0 21.5 39.1 16 69.0 25.0 36.2 22 76.0 25.5 33.6 30 87.0 30.5 35.1 May 7 64.0 28.0 43.7 14 60.0 26.0 43.4 21 24.0 13.5 56.4 28 0.0 0.0 0.0 MEAN 28.8 12.8 43.6 123
Table 17. Seasonal precipitation and temperature data from Salyer and Honor Camp 42 during recorded years of measurement (From United States Department of Commerce, 1949-1967, and California Department of Water Resources, 1961-1968).
SALYER PRECIPITATION TEMPERATURE IN INCHES IN DEGREES F.
Month Mean from Total during Mean from Mean during 1949 to 1967 1966-1967 1961 to 1967 1966-1967
Nov. 6.57 7.90 -- --
Dec. 9.64 9.39 44.7 44.1
Jan. 10.89 12.55 43.6 41.3
Feb. 7.25 0.88 44.1 46.5
March 6.13 6.44 44.4 41.5
April 2.87 4.06 46.4 40.2
May 1.76 0.78 49.1 52.0
TOTALS 45.11 42.00 MEANS 45.4 44.3
Temperature data from 1961 to 1963 are unpublished and were obtained directly from Honor Camp 42. Table 18. Depth and water content of snow on Anthony Peak in Tehama County (elevation 6,200 feet) from 1946 to 1967 (From Calif. Dept. of Water Resources, 1965-1967).
DEPTH AND WATER CONTENT IN INCHES February March April May Year Date Depth W.C. Date Depth W.C. Date Depth W.C. Date Depth W.C. 1946 1-29 63.3 30.7 3- 5 73.9 35.0 3-26 74.7 33.9 5- 2 40.5 21.7 1947 2- 3 23.1 6.8 2-27 14.2 6.1 4- 1 32.0 13.8 5- 1 0.0 0.0 1948 2- 2 0.0 0.0 3- 3 15.0 7.1 4- 1 45.2 17.0 5- 3 63.7 28.4 1949------2-25 68.9 25.6 4- 5 89.9 38.0 4-29 45.7 20.1 1950 2- 1 59.8 25.9 2-27 65.4 32.1 3-28 82.5 36.1 ------1951 1-26 40.1 18.0 2-26 46.0 20.7 4- 1 43.3 21.5 4-30 13.6 4.0 1952 1-29 115.8 45.6 3- 4 115.5 33.0 4- 7 117.4 41.1 4-29 79.8 42.9 1953 2- 2 63.5 29.0 2-26 55.2 28.4 4- 1 72.3 35.6 4-30 58.1 27.4 1954 1-30 48.8 20.3 2-26 55.9 24.7 3-31 58.6 26.3 4-27 23.1 10.2 1955 2- 2 60.6 18.6 2-25 45.3 18.8 3-31 47.0 20.2 4-29 58.2 22.6 1956 1-28 75.8 27.4 3- 1 125.6 49.7 4- 3 95.0 47.6 5- 9 64.2 35.5 1957 1-29 42.4 14.2 3- 1 33.7 14.8 4- 2 49.4 24.4 5- 3 23.6 11.1 1958 2- 5 77.0 27.7 2-27 70.7 30.6 4- 4 149.9 48.1 4-25 98.7 47.9 1959 1-26 19.2 6.7 2-25 66.6 23.6 3-27 41.3 18.6 ------1960 1-29 41.6 15.3 2-25 58.0 26.0 ------4-28 38.5 14.5 1961 1-25 15.0 6.0 2-27 25.5 11.9 3-28 62.4 25.0 4-25 47.6 17.8 1962 1-25 40.3 15.1 2-27 77.0 29.9 3-29 99.5 40.6 4-25 45.3 20.6 1963 1-25 0.0 0.0 2-27 0.0 0.0 3-26 16.4 5.1 4-29 53.6 26.5 1964 1-29 59.0 18.3 3- 2 49.5 22.2 3-27 62.2 26.2 5- 5 29.6 11.7 1965 2- 2 60.7 28.1 2-26 52.3 25.7 4- 1 50.2 26.9 5- 4 31.8 17.7 1966 2- 3 84.8 32.3 2-28 105.6 42.4 4- 4 88.3 44.7 5- 3 50.2 27.6 1967 1-31 54.2 20.8 2-24 44.9 20.2 4- 4 85.5 32.0 4-28 118.7 41.9 MEAN 49.8 19.4 57.5 24.0 69.7 29.7 49.7 22.5 125
Table 19. Monthly temperature measurements on Horse Mountain during the winter of 1966-1967.
TEMPERATURE IN DEGREES F.
Average Average Percent of time that Month Mean minimum maximum temp. exceeded 32°
Dec. 32.4 40.5 36.2 62.7
Jan. 31.4 40.1 35.8 67.8
Feb. 35.9 46.7 41.0 80.0
March 28.5 38.7 33.1 47.1
April 24.5 34.3 29.2 11.8
May 39.7 54.0 46.0 86.4
MEAN 32.1 42.4 36.9 59.4 126
Table 20. Temperature and solar radiation data used in regression relating weekly solar radiation to mean daily temperature for weekly period.
TEMPERATURE IN SOLAR RADIATION DEGREES F. IN LANGLEYS Weekly period Mean daily Total
2/11-2/17 35.8 1,307.3 2/18-2/24 40.4 2,337.3 2/25-3/ 3 35.5 1,927.9
3/ 4-3/10 40.6 2,376.9 3/11-3/17 30.6 765.9 3/18-3/24 34.4 1,399.7 3/25-3/31 27.9 1,254.5
4/ 1-4/ 7 31.9 831.9 4/ 8-4/14 29.0 884.7 4/15-4/21 26.7 277.3 4/22-4/28 28.8 1,188.5
4/29-5/ 5 36.9 2,905.1 5/ 6-5/12 40.8 1,861.9 5/13-5/19 56.0 3,671.0 5/20-5/26 52.3 3,935.1 5/27-6/ 2 37.2 2,099.6
MEAN 36.6 1,814.0
Computed by measuring the total chart area for the seven day period in square centimeters (229 cm. sq.) and dividing this area into 30,240 gram cal./cm. sq. (7 days x 1,440 min./day x 3 gram cal./cm. sq. = 30,240 gram cal./cm. sq.) to determine the chart constant, which was 132.05 gram cal. The chart constant was then multiplied by the area in square centimeters under the inked curve on the pyrheliograph chart. This area was measured with a polar planimeter. 127
Table 21. Snow quality measurements on Horse Mountain from January to May 1967.
SNOW DEPTH SNOW QUALITY IN PERCENT IN INCHES One-thir Two-thirdsdepth Date Total d depth Mean
January 7 17.0 83.2 -- 83.2 14 12.0 -- 76.7 76.7 21 21.0 100.0 100.0 100.0 29 22.0 94.3 93.8 94.1
February 4 24.0 87.6 95.5 91.6 12 16.0 82.2 92.8 87.5 18 22.0 97.0 96.8 96.9 26 22.0 99.1 98.2 98.7
March 4 20.0 99.5 99.7 99.6 11 42.0 100.0 100.0 100.0 19 36.0 100.0 100.0 100.0 27 33.5 100.0 95.0 97.5
April 2 57.0 100.0 92.5 96.3 9 55.0 93.4 96.8 95.1 16 69.0 100.0 100.0 100.0 22 76.0 100.0 100.0 100.0 30 87.0 100.0 100.0 100.0
May 7 64.0 86.3 78.2 82.3 14 60.0 80.0 84.0 82.0 21 24.0 80.6 82.5 81.6
MEAN 39.0 93.9 93.8 93.2
Sampling depth in relation to total depth of snow cover on sampling date. 128
Table 22. Description of formulas used in computing t values.
A) Formula to compare two groups of unequal sample size:
where: = the difference between the twc group means. = the size of each sample. = the pooled sum of squares.
The equation is set up as follows in using the above formula to compute the t value for comparison of basins for snow depth on February 18th (Table 7, page 81):
B) Formula to compare two groups of equal sample size:
where: = the same as above.
The equation is set up as follows in using the above formula to compute the t value for comparison of ski slopes and adjacent forest for water equivalent on February 18 (Table 8, page 83): 129
Table 23. Average snow measurements in the study basins on Horse Mountain from January to May 1967.
MEAN SNOW MEASUREMENT MEAN SNOW MEASUREMENT IN INCHES IN
a UNDEVELOPED BASIN Sampling Water Waterater Depth date equivalent equivalent -- January 7 14.3 4.7 -- 14 -- -- 11.2 4.9 16.1 6.2 February 4 19.7 7.5 18 14.0 5.7 18.6 7.4
March 4 12.5 5.4 17.1 7.1 19 -- -- 32.8 12.3
April 2 41.6 13.0 49.7 15.3 22 -- -- 63.5 20.8 30 65.4 23.0 66.8 24.0
May 14 40.1 17.4 41.1 18.2 21 9.2 4.5 12.8 6.2
MEAN 26.7 10.0 33.3 12.4
Average of 30 measurements on each sampling date.
Average of 15 measurements on each sampling date.
Average of 15 measurements in forest adjacent to slopes. 130
Table 24. Average snow measurements on ski slopes and in the forest adjacent to slopes on Horse Mountain from January to May 1967.
MEAN SNOW MEASUREMENT MEAN SNOW MEASUREMENT IN INCHES IN INCHES a/ ON SKI SLOPES IN FOREST Depth Sampling Depth Water Water date equivalent equivalent
January 7 15.0 4.9 13.6 4.5
February 18 15.5 6.6 12.4 4.7
March 4 13.9 6.3 11.0 4.5
April 2 42.3 13.9 40.9 12.0
April 30 65.4 24.2 65.3 21.9
May 14 42.0 18.7 38.3 16.1
May 21 10.0 5.1 8.4 3.9
MEAN 29.2 11.4 27.1 9.7
TABLE MEAN: Snow depth 28.2 Water equivalent 10.6
Average of 15 measurements on each sampling date. 131
Table 25. Average snow measurements from each sampling point on Horse Mountain from February 18th to May 21st 1967.
AVERAGE MEASUREMENT IN INCHES FROM SIX SAMPLING DATES Snow sampling Snow Water equivalent Snow density point depth of snow in percent
1 27.0 9.5 39.8 2 37.6 15.3 43.3 3 34.1 13.6 42.0 4 33.8 12.8 40.5 5 46.4 18.4 41.4
6 40.8 17.2 43.9 7 31.3 12.4 41.1 8 24.0 9.2 42.3 9 26.6 11.1 42.7 10 23.9 10.0 43.4
11 32.5 12.8 41.4 12 23.5 9.5 42.5 13 29.8 11.8 41.4 14 25.4 9.8 40.2 15 36.1 13.7 39.8
16 35.9 13.5 40.1 17 19.8 6.2 30.0 18 24.3 8.7 36.9 19 20.7 6.5 33.9 20 24.7 8.5 36.7
21 26.8 9.3 35.1 22 32.5 11.7 37.3 23 40.0 14.8 39.1 24 41.7 15.4 37.5 25 39.0 15.0 40.4
Sampling dates were: February 18th, March 4th, April 2nd and 30th, and May 14th and 21st. 132
Table 25. (continued)
AVERAGE MEASUREMENT IN INCHES FROM SIX SAMPLING DATES Snow sampling Snow Water equivalent Snow density point depth of snow in percent
26 34.6 13.2 40.9 27 29.4 10.1 37.3 28 23.8 7.7 31.2 29 17.7 5.6 29.8 30 30.0 11.6 42.4
31 29.9 14.8 41.4 32 52.4 20.6 40.4 33 52.8 21.2 41.3 34 22.4 7.6 36.2 35 47.1 19.1 42.2
36 49.2 19.6 43.1 37 43.9 16.7 39.8 38 17.5 5.2 31.9 39 19.3 6.6 36.5 40 19.4 6.7 36.4
41 37.7 13.9 38.8 42 23.5 8.2 35.9 43 28.1 10.8 41.5 44 42.7 17.6 42.6 45 29.3 10.5 38.6
MEAN 31.8 12.1 39.1
Sampling dates were: February 18th, March 4th, April 2nd and 30th, and May 14th and 21st. 133
Table 26. Recreation use on Horse Mountain during the winter of 1966-1967.
NUMBER OF DAYS NUMBER OF RECREATIONISTS Snow cover Slopes Month Skiers Snowplayers allowed skiing used
December 3 1 60 50
January 13 5 350 90
February 14 4 280 120
March 27 12 840 230
April 30 8 560 160
May 14 4 290 30
TOTAL 101 34 2,380 680
Coincides with the number of days when rope tows were in operation.