Found near landward edge of inter-tidal marsh, along the bay on the San Francisco peninsula.

I'm thinking this is in the family Dolichopodidae, and in the genus Paraclius (or, less likely 2nd choice, Mesorhaga). There are 15 species of Paraclius appearing on this recent Dolichopodidae Checklist. Details behind this ID attempt are given below. Hoping someone with expertise in this group can correct or confirm my ID here. I'd also very much appreciate any feedback from those with the interest (and patience:-) to follow through the details of my putative keying sequence below. Thanks!

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I did my best to key this in the "Manual of Nearctic Diptera"(1)(Vol I, 1983), now easily accessible online as a PDF. (Hooray!) I'm nearly certain this is in the family Dolichopodidae (gestalt and circumstantial cues are strong, although keying to family in MND(1) wasn't totally clear for me...that's why I'm making initial post here to "ID Request" page.)

Assuming this is indeed Dolichopodidae, I did my best to work through the key to genera (pg. 628 in MND(1)), modulo a few potentially treacherous key breaks which I'm hoping I navigated correctly...based mainly on the good agreement of the wing venation for Paraclius (see Fig. 31 on pg. 630 in MND(1) or this MCZ image).

My "2nd choice" ID here was due to my hesitance to unequivocally interpret the first key break, namely:

1) Vertex of head deeply excavated as seen from anterior view (Fig. 2). Scutum often as wide as long.......2; versus

1') Vertex of head not or only slightly excavated (Figs. 3-8). Scutum never as wide as long.......5

You can best see the "excavation" in last image in this series. It seems "slight" to me, rather than "deep". But even with reference to Fig. 2 on p. 629 of MND(1), I'm hestitant here...partly because I don't have a good "head-on view" image. The scutum here is slightly longer than wide...though, read carefully, that character pair in the couplet is not very definitive—note to the qualifier "often". (I omitted a third character from the couplet that seem even less definitive.) So I think the 2nd choice is the way to go, but if I do go with "deeply excavated", I get to genus Mesorhaga at the very next couplet [i.e. 2): Vein M unbranched].

So, returning to the (seemingly better) choice, "vertex not or only slightly excavated" in couplet 1), I navigated through the following sequence of couplet steps:

5) C continuous to tip of M; M not weak, and not discontinuous in last part. [See 5th image in this series.]

6) R4+5 and M nearly parallel (Fig. 33) or converging (Figs. 27-32) beyond crossvein dm-cu; M ending at most slightly behind wing tip. [Again, see 5th image in this series.]

9) Mid or hind femur with distinct pre-apical bristle on anterior to anterodorsal surface. [See 1st & 5th images in this series.]

18) Scape with one or more distinct setae on the dorsal surface, sometimes only with one or two at tip (Figs. 10, 19). [Perhaps visible in (enlarged) 4th & 2nd image of this series, though bristles there may actually be attached to pedicel. This is a (hopefully non-fatal) weak link in the keying sequence here. I'm hoping it's vindicated by the very good agreement in wing venation with final result below.]

19) First flagellomere without a projection below; arista usually dorsal or subapical. Abdomen not flattened dorsoventrally. [Opposing choice can be eliminated as it goes to genus Hypocharassus on the east coast of US, with a large distinctive and conspicuous "hook-like" projection on 1st flagellomere (see Fig. 19 on pg. 629 of MND(1)). No such hook here...I think it would have been visible in 3rd, 4th, and 6th images.]

20) Acrostichal setae present. [Best seen in 4th (and 5th, barely!) images.]

21) First tarsomere of hindleg without bristles above. [Visible in images 1-5.]

22) Lower margin of face nearly straight or recessed. [An admitted weakly supported choice here, made from comparing my 4th image with Fig. 8 (pg. 629 of MND(1)) for the opposing couplet choice: "Lower margin of face rounded, projecting downward......Tachytrechus".]

23) Upper and lower hairs of arista not longer than lateral hairs. [There seem to be no hairs on the arista, see 3rd and 6th images in series. The opposing option in this couplet "Upper and lower hairs of arista much longer than lateral hairs" and it's supporting Fig. 10 (pg. 629 of MND(1) don't match my specimen, but this is another iffy step in my keying sequence.]

24) R4+5 and M distinctly convergent beyond crossvein dm-cu (Figs. 30,31). [See 5th image in series...this fits very well!]

25) M distinctly bent beyond crossvein dm-cu (Fig.31), or hind femur with a second smaller pre-apical bristle antero-ventrally. [See 5th image in series, for both medial vein shape and 2nd pre-apical bristle (look at right hind leg, or barely visible "nub" on left hind leg).]..........Paraclius