This is a very well designed and described study of the composition of alpine soils in the SW USA. The focus of the study is on whether weathering local bedrock or imported eolian dust is the principal contributor to soil formation here. The study makes a convincing case for the dominant (but not exclusive) role of eolian dust. Although not a new concept, the originality of this work lies in the multitude of sites considered, the relatively large geographic area covered, and the range of lithological substrates represented.

I have marked many (mostly minor) comments in the edited PDF, which should make the paper clearer to the reader.

The three most substantive points I'd like to stress here are as follows.

1. I would like to see a more detailed description of the meteorological conditions of the area, particularly where it comes to wind and aridity parameters (dominant wind directions, strengths, seasonality; precipitation and humidity values, seasonality?).

2. This should logically extend to what is known of the geochemistry and mineralogy of the most obvious source areas for eolian dust likely to be transported over, and deposited on, the mountain region considered. Here I would like the authors for instance make use of the USGS soil geochemical landscape survey dataset (https://mrdata.usgs.gov/ds-801/; https://doi.org/10.3133/ofr20141082; https://doi.org/10.1144/geochem2022-031).

3. The paper is quite long and much detail could be placed in the supplement. For instance the Methods could almost entirely be moved there, with minimal loss of readability.

Other than that, this is a very good contribution to understanding soil formation and putting implications into perspective. I commend the authors on an interesting and well-constructed manuscript

This is a very well-designed and well-executed study, and the manuscript is thorough and well-written. My comments are all minor and I think this will be a very valuable contribution to the literature on dust deposition in mountainous regions. The important finding in this study is that across a very wide geographic range and across multiple bedrock types, dust plays an important role in soil formation in the Southwestern US. Because of dust deposition, the soils are much more fertile than they would be otherwise. Although the argument and methods are not novel, the strength of this study comes in the broad geographic range and the interesting comparison across bedrock types.

My main comment has to do with making the site variability more apparent in the text, tables, and figures. The site numbering system is not very intuitive, so it was challenging for me to remember which site was which when working through the manuscript. This is especially the case for all of the figures where the sites are numbered from highest to lowest (even though this does not seem to correspond to any site characteristics). I think it would help if the sites could be arranged from east to west (as they are described in the Study Area section), and if the bedrock could somehow be indicated on the figures – this would be especially helpful for Figures 5 and 11.

Specific comments:

Line 135: How deep were the soil samples collected? It seems like they were all surface soil samples given the difficulty in sampling soil in this environment, but it would be helpful to state an approximate depth or depth range for the soil samples.

Line 170: The sentence about the two size fractions doesn’t make sense, or maybe the sentence is missing a phrase. Make sure that it is clear that the <63um fraction was considered most likely to represent exotic mineral dust.

Line 183: “composite sample for collector” is a confusing phrase. Rephrase for clarity.

Line 193: There is an extra ‘were’ in this sentence.

Methods in general: This section contains very detailed analytical methods that could be moved into a supplemental file. Also, in the site description, it would be helpful to include information about known sources of dust in the region.

Lines 343-346: It is unclear which type of samples these values are for. Are you reporting across the dust, soil, and rock samples? Or are these values for one type of sample?

Lines 537-552: It might be helpful to show some of the correlations between soil fertility and dust characteristics – like the correlations mentioned with calcium. For me, this would have been more effective than looking back to Table 2.

Figure 1: The site locations are shown with yellow stars, not yellow triangles as the caption states.

Table 1: Include the dates of collection or the length of deployments in the table. It would be helpful if Table 1 could capture all of the deployment information written out in Lines 130-134. It would be helpful to visually see how the 22 samples are distributed across sites and seasons.

Figure 4: Is it possible to use a ternary diagram with lighter cross-hatching? Especially when printed at a smaller size, I am worried about the legibility of the points on top of such a dark background.

Either Table 2 or Figure 5 could be moved to a supplemental file.

Figure 6: It seems like summer21 samples have considerably more illite, kaolinite, and mica compared to the other dust samples. Is this a real difference, and if so, any ideas about why this might be?

Table 4: What does the Dust sample with no date refer to? Is this some kind of composite sample?

Figure 11: Use “Site” instead of “Collector” along the x-axis?