A GIS Based Description of the Lake Bonneville Bench Region of Cache County, Utah.

TRAVIS L CLEMENTS

MARGARET CORTSEN

TAKAHISA OTA

INTRODUCTION

The design of our project is to look at the Lake Bonneville bench region of Cache Valley with an emphasis on the eastern benches that skirt the Bear River Range of the Rocky Mountains. Physically, the Lake Bonneville benches are recognizable with the naked eye throughout the valley, but their impact on the region envionmentally, economically and even socially sometimes is not as apparant. While providing flat, fertitle land suitable for farming and residential purposes, they also exist as a stepped barrier between the valley floor and the mountains with their steep, almost uninterupted, faces. The benches also affect the climate and provide scenic outlooks to the graben-formed valley below.

Our purpose is to describe in a meaningful way the presence of the Lake Bonneville benches in Cache Valley and their resulting influence on the varied attributes of the region. We will look at physical, economical and social aspects, concentrating on the benches skirting the eastern rim of the valley. Due to data availability, our study is limited to the Utah side of Cache Valley (Cache County) with little consideration beyond.

HYPOTHESIS

The Lake Bonneville bench region should stand out from its surrounding geography in several ways. Besides being visible due to its elevation characterisitics, it should also be evident indirectly through roads, waterways, city development and planning including land ownership and land value, climate, soils and vegetation.

Roads should tend to parallel the benches rather than disect them. A watercourse, such as a river, should cut through the bench perpendicularly to reach the valley floor, though man-made canal systems could use the gently sloping bench tops for irrigation and culinary pruposes. The pioneer establishment of the region placed most towns on the valley floor to avoid the unnecessary toil created by increased slope. Cars and other technologies should allow for development to press upward onto the benches. The bench region should also create a psuedo-independant climate differing from the mountains above and the valley below. This would also make the bench region a transition zone for vegetation and possibly even soils.

DATA

PROCEDURE

Individual Benches

On the east the bench is seen cutting deep into Blacksmith Fork and Logan canyons and a little less further north into Smithfield canyon. Also, notice the broadening effect of the bench at the canyon mouths due to sediment deposit.

Combined Bench Region A comparison of the vegetation layer through the two bench layers shows how much clearer the combined bench layer is in displaying the characteristics of the region. All of our subsequent analysis was done using the combined bench GIS layer.

The vegetation layer gave us our first insight concerning the transitional nature of the bench. At the lower elevation the vegetation is relatively homogeneous. As you move eastward up the bench, not only does the type of vegetation change but the variability also increases dramatically.

We digitized two maps, the first a Bonneville Lake Level map put out by the Utah Geological Survey, the second a Freeze-Free Season map produced by the Utah Climatology Office. Both maps contained state-wide data but we only digitized our area of interest. After labeling they were brought into ArcView for observation. Due to incompatible projection problems we were not able to overlay the bench region layer for further analysis. The maps revealed climatic characterisitics and a lake level reference for the benches.

RESULTS

At this stage it became a matter of finding appropriate GIS layers to study which would help reveal the characteristics of the bench region. We also found that by looking at the layers in different formats, often some trends could be seen more clearly. Look at the inverted view of geology layer on the east bench. The bench region has been blacked out to highlight the surrounding characteristics. Then, by putting the bench characteristic side-by-side, the nature of the entire region can be seen much more clearly.

Cache valley is a graben, formed by faults on either side that allow the center to sink. As centuries pass the lower valley floor is covered with sediment from the mountains. This being the case we expected to see well defined differences between the mountains and the valley. The bench region is obviously in this transition zone.

If you look at the entire valley with the faults, the benches are quite clearly defined as aspects of the valley's formative processes. Notice on the western edge of the valley how the bench is outlined on both sides by faults.

Valley Benches with Faults

We wanted to start back with vegetation cover at this point and use it as a reference for the other aspects that follow. By looking at the inverted bench view (black bench), the vegetation characteristics are easier to see than before with only the bench region being visible.

The bench region appears to be an area of concentrated change in both the variablitly and type of vegetation. There are other aspects that must be considered when dealing with vegetation also. We brought in soil data to compare and found some interesting similarities.

The inverted layout (black bench) fails to show the signifigance of the soil distribution, but when seen against the isolated bench, becomes more apparant. The bench's soil make-up is relatively homogenious, which is consistant with the vegetation, but we can also see that the variability of the soils on the bench appears to be introduced from the canyons, especially Smithfield canyon. If you compare the soils against the vegetation, though at different scales, you can see that the variablity of the vegetation appears to have a strong positive correlation with the changes in soil make-up.

The availibility of running water on the bench is somewhat unclear. Logan river is the largest river draining the eastern mountains and crossing the bench. It has been altered by man for irrigation purposes and canals can be seen tracking parallel to the mountains along its' accomodating surface. Though not available from digital data sets yet, further canal construction is continueing today, especially southward from Logan canyon.

Another key element to vegetation cover that we had available to us was the information digitized from the Freeze-Free Season climatology map. The regions are cut into seasons according to an average length of above freezing temperatures during the summer months. The bench region appears light orange with dark orange being warmer. The seasons shorten to either side of the bench.

The longest growing season in the valley averages from 160-180 days at the mouth of Logan canyon. The rest of the bench averages from 140-160 days while at the middle of the valley floor the growing season can be as short as 80-100 days. The lake bench region has provided an abnormally long growing season for a large area of the valley. Depending upon the quality of the soil and the availability of water, the bench region could have far and away the best agricultural potential.

The future of the bench region lies outside of the State's hands. Areas appearing green are already designated as state or nation forests. Efforts to maintain it as an agricultural or range resource will have to be approached from the city and county levels. An ownership map shows just how little influence people outside of the region have.

Bench Ownership

Cache Valley, consistant with the most of Utah, was settled by mormon pioneers who planned their communities extensively and built their towns on the valley floor. This pattern has been obscured lately by recent developmental trends that dictate the direction of growth towards and onto the foot of the mountains. A view of the roads through the bench layer reveals to what extent all of the communities in Cache County are spreading up and across the benches.

The Lake Bonneville benches of Cache County are the most dominating feature of the region besides the mountains themselves. Their influence and impact upon a modern day descritpion of the valley can not be overstated.

The bench region provides a clearly defined region of transition for vegetation, soils, geology and even settlement. The characteristics of the valley and the mountains differ greatly, changing abruptly at the boundry of the bench. The bench is also defined in it's level of homogeneity, an attribute not expected in a transitional zone. The gently sloping steps are covered by a small variety of fertile soils and inhabiting grasses and plants. While the nearly level ground and excellent view of the valley are desireable for future development, the bench also represents the longest growing season in the area and the highest potential for geologic distrubances such as earthquakes and slides, due to the proximity of active faults.

The future of the bench region is almost completely in the hands of local residents and businesses. If there is a desire to maintain the benches as a winter range or just to keep them from becoming like the over-housed benches of Bountiful and Salt Lake City, action needs to be taken soon. The evidence shows that growth trends will continue to dictate development along the bench.