A Quantitative Flora of Willow and Tahquitz Creeks, San Jacinto Mountains

Tom Chester, Dave Stith, William Schlegel, RT Hawke, and Mike Crouse

Table of Contents

Geography of the Survey Area
Survey Details
Important Caveats
Checklist for Willow Creek and Lower Tahquitz Creek
Appendix: Observed Deer Browse Plants

This is a first draft page of this flora. The major incompleteness is the comparison to previous vouchers, which needs updating from a comparison to Hamilton's vouchers, and from vouchers placed online in the last two years. This work will be done over the next several weeks.

Other items to add:


We present a quantitative vouchered flora, containing 180 native taxa and 5 non-native taxa, from a survey of 92% of the entire length of the main courses of Willow Creek and Tahquitz Creek in Tahquitz Valley in the higher-elevation San Jacinto Mountains. Of the 185 taxa in the flora, 95 are riparian species. The other 90 were non-riparian species encountered during the course of the survey in the vicinity of the creeks.

Fifteen separate surveys were done on 15 days from 28 July through 1 October 2009, covering 6.25 miles of creek in total. Only 0.56 miles of the main creek courses remained unsurveyed, all in uppermost Willow Creek. Estimates of the number of each species, and the number of locations in which each species was found within each survey, were made in each of the 15 surveys.

Over half of these taxa, 102 of the 185 taxa, 55%, do not have any online vouchers from Tahquitz Valley. However, Michael Hamilton may have vouchered many of them from his survey in 1980-1982; we will compare against his list as soon as we examine his vouchers to update the determinations.

The survey found three native species that are new records for the San Jacinto Mountains flora: Ageratina occidentalis, Bromus ciliatus and Muhlenbergia andina. Ageratina occidentalis, a disjunct from the Sierra Nevada with only a single other location in southern California, was found only in a single remote location with difficult access. In contrast, Bromus ciliatus and Muhlenbergia andina are fairly widespread, being found in 11 and 9 of the 15 surveys, respectively, making it surprising that they had not been vouchered previously.

The survey found many more native species that are new records for Tahquitz Valley.

In addition to the floral survey, we conducted a census of all lemon lilies, Lilium parryi, in these creeks. We found 2,662 individual stalks, which almost doubles the known extant number of lemon lilies in the world in their native habitat.


This is a quantitative vouchered flora for Willow Creek and Tahquitz Creek in Tahquitz Valley in the higher-elevation San Jacinto Mountains. This flora has been compiled from 15 separate surveys done on 15 days from 28 July 2009 through 1 October 2009, with the surveys usually spaced every fourth day. Estimates of the number of each species, and the number of locations in which each species was found within each survey, were made in each of the 15 surveys.

This project was not begun as a flora project; its genesis was in Dave's desire to do a lemon lily census in Willow Creek, counting every lemon lily stalk (see lemon lily census). Tom signed on quickly to this project, and of course compiled a flora of the area, with Dave, as we surveyed for lemon lilies. Additional botanists aided us in some of these surveys, as detailed below. Those who participated in at least 20% of the surveys are joint authors of this flora.

This survey turned out to be very interesting in a number of respects. First, it totally changed our thoughts about the healthiness of the lemon lily population at San Jacinto Mountain.

Second, we became very familiar with the species that grow in wet areas here. We had only infrequently come across many of these species, since our previous surveys of trails and ridge tops contained few of them. In particular, we had never really become expert on some of the grasses and sedges before. Encountering these species every fourth day, and studying them in between, vastly increased our knowledge of these sometimes-challenging species.

Third, we were absolutely delighted to come across a number of species that we knew were supposed to be present at San Jacinto Mountain, such as fireweed, Epilobium angustifolium, that we had never seen elsewhere.

Fourth, the most surprising result of the survey was finding three native species that had never been recorded anywhere at San Jacinto Mountain before! Before we did these surveys, we would never have thought that these two creeks represented virgin territory for botanists.

But we quickly realized that it was no picnic to explore these creeks in most places. It is a strenuous hike just to get to these creeks from below, and surveying the creeks requires the ability to navigate obstacles on a regular basis, and sometimes climbing up or down rock walls or steep slopes to get around them. Such exploration has a high potential for twisted ankles, falls and stab wounds; nearly every one of us participating in these surveys suffered at least one of those injuries. After one of the expeditions, we commented that it would be easy to return to where we ended that survey, to begin the next survey, simply by following the trail of blood left by us. One of us almost literally lost his shirt when a dead willow branch ripped it nearly in half.

The difficulty of the exploration is summarized by these numbers: it took us 15 separate trips to cover 6.25 miles of creek. Our average survey coverage per day, in the ~3 hours available for botanizing after the strenuous hike to get to the creeks, was just 0.4 miles of creek, a rate of ~0.15 miles per hour (0.2 km/h).

Our speed was determined in part by the time needed to count 2,662 lemon lilies, with densities as high as 1,700 lilies per creek mile in one stretch. The floral survey was probably made significantly more complete by doing the lemon lily census, since it forced us to explore the creekbed in much more detail than we probably would have done if we were just compiling a flora.

This is a quantitative flora since immediately after each survey we estimated the total number of plants we saw for each species, and the total number of locations in which we saw each species. Furthermore, since these two creeks represent the vast majority of the riparian areas in Tahquitz Valley, this is a nearly-complete census of the entire riparian area of Tahquitz Valley (meadows are a separate habitat that was only partially surveyed here).

We also recorded non-riparian species in the vicinity of the creeks, and along our return trip to the nearest trail. Thus we also recorded a sample of the non-riparian species in the area of each survey. Those species are presented here as well, but the numbers reported for them are not as meaningful as the numbers reported for the riparian species, since our sampling of the habitats of those species was not complete. In particular, species that live on ridges are almost completely absent from this sample.

In the checklists presented below, we have either noted which species are found in riparian areas, and which are not, or have presented separate lists for riparian and non-riparian species.

An Analysis of the Flora of Willow and Tahquitz Creeks will be given separately.


The following large-scale map shows the location of Willow and Tahquitz Creeks in southern California, with the surveyed portions denoted as heavy blue lines in the upper middle portion of the map, to the east of the town of Idyllwild:

These creeks drain the generally-east-northeast-facing desert side of the main ridgeline of the San Jacinto Mountains, in an older terrain still preserved above the steep escarpment above the desert. There is no evidence that this area was ever glaciated (see also Extreme southwestern margin of late Quaternary glaciation in North America: Timing and controls).

The following maps show the location of the floral area targeted here in detail:

In the middle map above, the individual surveys are color-coded and numbered in order of descending elevation, with the prefix W for the Willow Creek portions, the prefix T for the Tahquitz Creek portions. A table below gives details on each individual survey. The last two maps above show the entire survey route for each trip, including the non-creek portion.

Geography of the Survey Area

Tahquitz Valley is a remnant of an older flattish terrain that is being eroded from three sides. Only its northern edge is largely protected from erosion by Tamarack / Round / Long Valleys, a similar flattish terrain.

Tahquitz Valley is bounded by a prominent east-west ridgeline scarp on its north, an eroded roughly north-south ridgeline on its west with Saddle Junction in its middle, a prominent roughly southwest-northeast ridgeline on its south, and an eroded northwest-southeast ridgeline on its east. See an outline of the valley on a topo map from the Berkeley Mapper.

In the Google Earth image below, looking up canyon, to the west, with north on the right, it is delineated by:

See also a map showing a larger area with labels; a map showing a larger area without labels; and a map from a perspective looking more straight down on Tahquitz Valley without labels. All these linked maps have the same orientation, with north to the right, and show the neighboring Tamarack / Round / Long Valleys to the north.

Using the perimeter drawn on this map, the Berkeley Mapper reports that Tahquitz Valley has a total area of roughly 6.56 square miles (4200 acres; 1700 hectares; 17.0 square km). Its perimeter is roughly 11.6 miles (18.6 km).

Tahquitz Valley has a maximum east-west extent of 3.5 miles (5.7 km) from Marion Mountain to the longitude of Caramba. Its maximum north-south extent is 3.1 miles (5.0 km) from the peak just west of Hidden Lake Divide to the latitude of the saddle between Tahquitz Peak and the ridge of Red Tahquitz.

Our survey spanned an east-west distance of 3.0 miles (4.9 km), and a north-south distance of 2.3 miles (3.7 km).

The elevation profiles of Tahquitz Creek and Willow Creek are given below for the surveyed portions:

The zero of the mileage scale in the above plot was taken from the point where the Pacific Crest Trail crosses lower Wellman Cienega, and thus for Willow Creek, the x-axis label could simply read Mileage from Wellman Cienega. In order to place Tahquitz Creek on the same scale, it was measured upstream from its confluence with Willow Creek, which for Willow Creek is 2.74 miles from Wellman Cienega. This accounts for the clunky x-axis label in the above plot; otherwise we would have had to use negative mileages from this point or from Caramba.

See also the elevation profile extended to one mile below the Caramba dropoff.

Willow Creek flows down an east-facing slope in its upper portion, and down a southeast-facing slope in its lower portion. It begins in the two disjunct portions of Wellman Cienega, a wet meadow at high elevation, 8880 feet (2706 m). Willow Creek contained flowing water throughout most of its course during our survey in August of a half-normal rainfall year. It was an unusual half-normal rainfall year, in which no rain or snow fell after 18 February 2009.

The elevation profile of Willow Creek is smooth overall, with few flat areas along its course except near its confluence with Tahquitz Creek. Its channel has many bouldery areas but few meadowy areas. What few meadowy areas it has are extremely small in size, patches measured in feet or meters, all of which were too small to actually denote them as meadows.

Upper Tahquitz Creek flows down a north-northeast-facing slope in its upper half. Below that, it flows northeast and then east along the bottom of its canyon, with the canyon walls orientated mostly along the creek. Unlike Willow Creek, Tahquitz Creek is dry at its head, with no water flowing in the summer at all. It picks up groundwater flow as it descends. Three side drainages join it as it descends, significantly augmenting its flow.

The elevation profile of upper Tahquitz Creek is punctuated by two flattish meadows, Little Tahquitz Meadow and Reeds Meadow, which are too small to be apparent in the large-scale elevation plot above. Upper Tahquitz Creek contains several smaller meadowy areas in addition to these two large meadows that again are too small to be denoted as meadows.

Lower Tahquitz Creek, from the confluence with Willow Creek to the lip of the escarpment at Caramba Camp, flows east-west overall, but with significant but small north-south meanderings. The canyon walls mostly follow the east-west trend. This section has a more gentle elevation gradient overall, but still has bouldery sections interspersed with flattish sections.

Survey Details

The 15 surveys analyzed here spanned 2280 feet (695 m) of elevation, from 8880 feet (2706 m) to 6600 feet (2012 m), along 2.3 and 2.4 miles (3.7 and 3.8 km) of the two main upper branches of Tahquitz Creek (Willow Creek and the main channel of Tahquitz Creek), and along 1.6 miles (2.5 km) below their confluence. The survey spanned an east-west distance of 3.0 miles (4.9 km), and a north-south distance of 2.3 miles (3.7 km).

Specifically, the surveys were from an elevation of 8880 feet (2706 m) on the northwest edge of Tahquitz Valley at the highest point of the Willow Creek Survey, and an elevation of 8300 feet (2530 m) on the southwest edge of Tahquitz Valley at the highest point of the Tahquitz Creek survey, down to an elevation of 6600 feet (2012 m) on the east edge of Tahquitz Valley. The northwest edge is just below the 10,000 foot (3050 m) elevation Marion Mountain - San Jacinto Peak ridge. The southeast edge is just below the ~8800 foot (2700 m) Tahquitz Peak - Red Tahquitz Peak ridge. The east edge is the lip of the dramatic steep escarpment to the sea-level desert below.

The habitat and plant communities are strikingly different at the three edges of the survey, due to elevation differences, rainfall differences, and slope aspects.

The following table gives the details for each of the 15 surveys. W1 is the highest-elevation Willow Creek Survey, W5 the lowest-elevation Willow Creek Survey, T1 the highest-elevation Tahquitz Creek Survey, T6 is the segment of Tahquitz Creek below the confluence with Willow Creek, etc.; see also maps showing each segment. The Creek Mileage on the scale described above.

LabelSurvey Date
Creek MileageSurveyed
Elevation (feet)Elevation

The time span of the survey was 65 days, from 7/28/09 to 10/1/09. The survey spacings were: every third day (two times); every fourth day (nine times); every fifth day (two times); and thirteen days (one time).

The participants in each survey were as follows:

Sort by Creek / Elevation Sort by Date
LabelDateParticipants LabelDateParticipants
W108/05/09Tom Chester, Dave Stith W307/28/09Tom Chester, Dave Stith, Mike Crouse
W208/01/09Tom Chester, Dave Stith, Mike Crouse W208/01/09Tom Chester, Dave Stith, Mike Crouse
W307/28/09Tom Chester, Dave Stith, Mike Crouse W108/05/09Tom Chester, Dave Stith
W408/08/09Tom Chester, Dave Stith, James Dillane, William Schlegel W408/08/09Tom Chester, Dave Stith, James Dillane, William Schlegel
W508/12/09Tom Chester, Dave Stith W508/12/09Tom Chester, Dave Stith
T110/01/09Tom Chester, Dave Stith T608/17/09Tom Chester, Dave Stith, Mike Crouse, RT Hawke, Shaun Hawke
T209/28/09Tom Chester, Dave Stith T708/30/09Tom Chester, Dave Stith, RT Hawke
T309/24/09Tom Chester, Dave Stith T809/03/09Tom Chester, Dave Stith, RT Hawke
T409/20/09Tom Chester, Dave Stith, William Schlegel, Pam Pallette T909/07/09Tom Chester, Dave Stith, William Schlegel
T509/16/09Tom Chester, Dave Stith, James Adams T1009/11/09Tom Chester, Dave Stith, William Schlegel
T608/17/09Tom Chester, Dave Stith, Mike Crouse, RT Hawke, Shaun Hawke T509/16/09Tom Chester, Dave Stith, James Adams
T708/30/09Tom Chester, Dave Stith, RT Hawke T409/20/09Tom Chester, Dave Stith, William Schlegel, Pam Pallette
T809/03/09Tom Chester, Dave Stith, RT Hawke T309/24/09Tom Chester, Dave Stith
T909/07/09Tom Chester, Dave Stith, William Schlegel T209/28/09Tom Chester, Dave Stith
T1009/11/09Tom Chester, Dave Stith, William Schlegel T110/01/09Tom Chester, Dave Stith

Tom Chester and Dave Stith participated in all 15 surveys; William Schlegel participated in four surveys; Mike Crouse and RT Hawke each participated in three surveys; and James Dillane, James Adams, Shaun Hawke and Pam Pallette each participated in one survey. For the authorship of this flora, we included everyone who participated in at least three (20%) of the surveys.

Important Caveats

Surveys are never complete, especially those done only once. It is therefore quite likely that at least a few species have been missed for a number of reasons.

The most likely source of incompleteness in this survey is missing annual species. This survey was done in late summer / early fall of a half-normal rainfall year. Furthermore, it was an unusual half-normal rainfall year, in which no rain or snow fell after 18 February 2009.

In particular, three annual monkeyflower species, Mimulus breweri, M. floribundus and M. guttatus, which are present in the drainages along the Devils Slide Trail in wet years, were totally absent from that trail this year. We would expect that at least some of these species would have been found in our survey in a wetter year.

We did find 20 annual species in our survey, including Mimulus pilosus, so not all annual species were missing. Annuals vary in their germination requirements, so we may have just found the annual species that were able to germinate in this peculiar, low-rainfall year.

Another significant source of incompleteness is missing species, or significantly underestimating the abundance of species, that were not in flower or fruit during our survey. In particular, we were quite surprised to find specimens of Calochortus invenustus in only one place in our survey, since we observed at least several other places with suitable habitat. Although we are pretty good at recognizing dead fruit stalks of this species, we found none in those other areas. But it is quite possible that this species did not flower well this year, or that deer or other animals ate the stalks.

Grasses and sedges might be more affected by this, since many grasses and sedges without flower or fruit are nearly impossible to identify correctly. Also, since we were learning some of the grasses and sedges as we did the survey, it is possible that some of these species went unnoticed in the earlier surveys since we had not yet developed an eye for discriminating them from the ubiquitous other members of these families.

One measure of the possible incompleteness of our survey is given in our Analysis of the Flora of Willow and Tahquitz Creeks. There we have given a list of species not found in this survey which were vouchered or otherwise expected to be present here.

Another source of incompleteness was our emphasis on the reliability of the determinations. If we could not identify a particular specimen with high reliability, we did not include it in the checklists. For example, we observed a single probable Cirsium specimen, consisting only of a basal rosette, that could not reliably be determined to species. We did not include this under any name since we could not be certain that it was even a Cirsium.

Some plants and taxa have been lumped together in the flora due to difficulties of separating them in the field, and one species has been separated into subspecies based on elevation as well as observing flowers:

We remind the reader again that this was a survey of the riparian zone of these two creeks, and hence this checklist is not complete for non-riparian plants in Tahquitz Valley.

Checklist for Willow Creek and Lower Tahquitz Creek

The plant checklist from our survey is presented in several different forms, since the total information is too large to easily be presented in a single checklist.

Most people will probably just be interested in the complete list of all observed taxa, including both the riparian species targeted here and the non-riparian species seen as well, with a basic numeric assessment of the abundance of each taxa.

Another list gives the detailed abundance of each species found in each survey, two numbers from each survey, a total of 30 numbers for each species. This list omits the family and common name, in order to fit in the abundance information.

The above lists are also broken into two lists, one composed only of riparian species and one composed only of non-riparian species.

Lists are also given sorted by plant abundance, for all species and separately by riparian status.

Another list gives the voucher information for each species.

Twenty two species have notes on their determinations, abundances, or have additional information given for them. The scientific name of those species, followed by a superscript + sign, is linked to an entry in a separate file giving those notes.

A separate page, Analysis of the Flora of Willow and Tahquitz Creeks, gives a list of species not found in this survey which were vouchered or otherwise expected to be present here.

The information below explains how each checklist is organized, and the meaning of the column headers.

Except for the checklist sorted by abundance, the Checklists are sorted first by category - ferns, dicots, and monocots - and then by family and scientific name. The Family and Scientific Name are from the 1993 Jepson Manual. An asterisk before the Common Name indicates a non-native taxon.

The other columns give the following information:

#SThe total number of surveys in which each taxon was found.

See Analysis of the Flora of Willow and Tahquitz Creeks for a histogram of the total number of surveys for each taxon.

#PlThis is our estimate of the minimum number of plants for each taxon in each of our surveys. The maximum value is 99 plants. The main intent of this column is to indicate the species for which we found few plants.
Sum #PlThis is the sum, over all 15 surveys, of the minimum number of plants for each taxon in each survey. Since it is a sum of minimum numbers, it is not a true estimate of the abundance for very abundant plants. The maximum value is 15 * 99 = 1485.
#LocThis is the minimum number of locations for each taxon in each survey. The maximum value is 9 locations. The main intent of this column is to indicate the species for which we found few plants or locations.
Sum #LocThis is the sum, over all 15 surveys, of the minimum number of locations for each taxon in each survey. Since it is a sum of minimum numbers, it is not a true estimate of the abundance for very abundant plants. The maximum value is 14 * 9 + 3 = 129, since the maximum value for one of the Willow Creek surveys was 3, instead of the usual 9, due to its short survey.
VThe number of vouchers for each taxon, with separate columns given for vouchers in Tahquitz Valley; vouchers above 6500 feet outside of Tahquitz Valley at San Jacinto Mountain, and the total number of San Jacinto Mountains vouchers at any elevation. If our voucher is a new record, an N is given in the Tahquitz Valley column.
RIf a taxon grows in riparian areas, including creeks, wet meadows, seeps, springs, or in moist drainages, a R is given in this column. Such a designation does not imply that a species grows only in such areas. For example, Carex fracta grows in dryish areas as well as wet areas.

Links to the Checklists for Willow Creek and Lower Tahquitz Creek

TypeAll TaxaJust Wetland TaxaJust Non-Wetland Taxa
Family Order, summary abundance dataAll
Family Order, detailed abundance data
Abundance Order, detailed abundance data
Voucher Information

Appendix: Observed Deer Browse Plants

Our survey covered some of the most remote parts of Tahquitz Valley. We saw abundant signs of deer, including a skeleton in Tahquitz Creek, abundant deer scat, abundant deer trails, and abundant deer beds. Interestingly, we did not see abundant browsing by deer. It is a little unclear to us how the amount of browsing we saw could support a significant deer population.

RT Hawke, who is familiar with the San Gabriel Mountains and the San Bernardino Mountains, commented that he had never seen so many signs of deer before.

We did not make a list of browsed plants as we did the survey, but we did photograph some of the browsing. From those photos, and from memory, these plants showed the most evidence of deer browse:

Voucher data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/).

We thank James Dillane, James Adams, Shaun Hawke and Pam Pallette for each helping with the field work for one of the 15 surveys.

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Copyright © 2009 by Tom Chester, Dave Stith, William Schlegel, RT Hawke, and Mike Crouse.
Commercial rights reserved. Permission is granted to reproduce any or all of this page for individual or non-profit institutional internal use as long as credit is given to us at this source:
Comments and feedback: Tom Chester
Last update: 27 October 2009