10:30 am PDT                                   days to Equinox: 9.35 days 2018-09-13 17:30 UT	10:45 am PDT                                   days to Equinox: 9.34 days 2018-09-13 17:45 UT
10:30 am PDT                                   days to Equinox: 8.35 days 2018-09-14 17:30 UT	10:45 am PDT                                   days to Equinox: 8.34 days 2018-09-14 17:45 UT
10:30 am PDT                                   days to Equinox: 7.35 days 2018-09-15 17:30 UT	10:45 am PDT                                   days to Equinox: 7.34 days 2018-09-15 17:45 UT
10:30 am PDT                                   days to Equinox: 6.35 days 2018-09-16 17:30 UT	10:44 am PDT                                   days to Equinox: 6.34 days 2018-09-16 17:44 UT
10:31 am PDT                                   days to Equinox: 5.11 days 2017-09-17 17:31 UT	10:46 am PDT                                   days to Equinox: 5.10 days 2017-09-17 17:46 UT
10:31 am PDT                                   days to Equinox: 4.11 days 2017-09-18 17:31 UT	10:47 am PDT                                   days to Equinox: 4.10 days 2017-09-18 17:47 UT
10:31 am PDT                                   days to Equinox: 3.11 days 2017-09-19 17:31 UT	10:46 am PDT                                   days to Equinox: 3.10 days 2017-09-19 17:46 UT
Solar Quarter Day 10:31 am PDT                                   days to Equinox: 2.11 days 2017-09-20 17:31 UT	Solar Quarter Day 10:46 am PDT                                   days to Equinox: 2.10 days 2017-09-20 17:46 UT
10:31 am PDT                                   days to Equinox: 1.11 days 2017-09-21 17:31 UT	10:46 am PDT                                   days to Equinox: 1.10 days 2017-09-21 17:46 UT

*: from September 13 until September 16, 2017 and again from September 17 until Spetember 21, 2018 I documented the shadow at Atlatl Rock each day starting at about 9:00 am PDT by taking pictures every ~ 15 minutes until the shadow on the petroglyphs at about 12:15 pm PDT was no longer visible as the whole area was in (self) shadow.

It turned out, that the best defined shadow line (in fall) occured at around 10:30 am PDT when the shadow was very stable and straight. After about 10:50 am PDT the shadow started its secondary movement downwards.

This combined observations cover the time nine days to one day before the fall equinox (which was on September 22, 2017 at 01:02 pm PDT and on September 22, 2018 at 06:54 pm PDT).