OK, downloaded and converted the .imq file to a .img, and used NASAVIEW to generate a GIF image.

There are a couple of other little features elsewhere in the image, but small beer compared to the main tract.

Image label contains the following:-

PDS_VERSION_ID = PDS3

FILE_NAME = "m1901170.img"

RECORD_TYPE = FIXED_LENGTH

RECORD_BYTES = 1008

FILE_RECORDS = 7043

LABEL_RECORDS = 3

^IMAGE = 4

SPACECRAFT_NAME = MARS_GLOBAL_SURVEYOR

MISSION_PHASE_NAME = "MAPPING"

TARGET_NAME = MARS

INSTRUMENT_ID = "MOC-NA"

PRODUCER_ID = MGS_MOC_TEAM

DATA_SET_ID = "MGS-M-MOC-NA/WA-2-SDP-L0-V1.0"

PRODUCT_CREATION_TIME = 2001-08-22T23:24:41

SOFTWARE_NAME = "makepds 1.9"

UPLOAD_ID = "UNK"

PRODUCT_ID = "M19/01170"

START_TIME = 2000-09-17T09:26:12.21

IMAGE_TIME = 2000-09-17T09:26:12.21

STOP_TIME = 2000-09-17T09:26:21.16

SPACECRAFT_CLOCK_START_COUNT = "653650000:238"

SPACECRAFT_CLOCK_STOP_COUNT = "N/A"

FOCAL_PLANE_TEMPERATURE = 245.2 <K>

GAIN_MODE_ID = "0A"

OFFSET_MODE_ID = "4"

LINE_EXPOSURE_DURATION = 0.602600 <MILLISECONDS>

DOWNTRACK_SUMMING = 2

CROSSTRACK_SUMMING = 2

EDIT_MODE_ID = "0"

RATIONALE_DESC = "Dune field monitoring "

DATA_QUALITY_DESC = "ERRORS"

ORBIT_NUMBER = 6834

OBJECT = IMAGE

LINES = 7040

LINE_SAMPLES = 1008

LINE_PREFIX_BYTES = 0

LINE_SUFFIX_BYTES = 0

SAMPLE_TYPE = UNSIGNED_INTEGER

SAMPLE_BITS = 8

SAMPLE_BIT_MASK = 2#11111111#

CHECKSUM = 16#0028675A#

END_OBJECT = IMAGE

END

No useful lats and longs there. As I recall one has to extract them from elsewhere in the endless heaps of files (All very clumsy and awkward, but that's life).

Here is the context image:

And a miniature version of the main image to show where it fits in. (note that I had to do a left-right swap of the mini image to get it to match)

In the context image, you can see the dark line along the ridgetop (I suspect I was wrong earlier with my 180 degree idea. That looks a LOT like a ridge crest)

Now all I need to do is find how to locate an image on Mars if I know WHEN it was taken by MGS...