The Zodiac stated "I am the murderer of the taxi driver over by Washington St + Maple St last night." on October 13th 1969, suggesting that this was his original intended murder site, which would have facilitated an exit north along Maple Street, before traveling east to Spruce Street and north into the Presidio park. The destination of Washington & Maple makes much more sense bearing in mind an escape via Spruce Street and Julius Kahn playground.
The Zodiac stated on November 9th 1969 "2 cops pulled a goof abot 3 min after I left the cab. I was walking down the hill to the park when this cop car pulled up + one of them called me over + asked if I saw anyone acting suspicious or strange in the last 5 to 10 min + I said yes there was this man who was runnig by waveing a gun & the cops peeled rubber + went around the corner as I directed them + I disappeared into the park a block + a half away never to be seen again." This description tallies with Spruce Street, which is situated approximately a 'block and a half away.' from the sighting of Officer Donald Fouke and Eric Zelms as they traveled west along Jackson Street. The Zodiac stated "The dogs never came with in 2 blocks of me + they were to the west". Arguello Boulevard, where Zodiac described the police cars and fire trucks and where the hive of activity was focused, is just over two blocks west of Spruce Street.
And finally Zodiac stated "there was only 2 groups of parking about 10 min apart then the motor cicles went by about 150 ft away going from south to north west." The only view of Arguello Boulevard from Zodiac's position in the trees adjacent to Spruce Street, is the section of road running northwest. In fact, it runs from south to northwest, just as the Zodiac stated. If he was in the park, concealed in the trees by Spruce Street, then everything he said would effectively be true. The reason the Zodiac only has an eyeline on this section of Arguello Boulevard, is that the rest is masked by trees, as it was in 1969.
We are fairly certain the Zodiac Killer used a vehicle to depart the scene in his first three attacks, but in the Presidio Heights murder of Paul Stine there is much doubt. Some people swear he had a getaway car waiting nearby, while others suggest he may have lived close by. What we do know, is the Zodiac Killer fled the scene on foot and claimed he entered the park - and for the purposes of this article - we shall take everything the Zodiac stated at face value and see where it leads us.
In the 'My Name is..Letter' mailed on April 20th 1970 the Zodiac stated "I have killed ten people to date. It would have been a lot more except that my bus bomb was a dud. I was swamped out by the rain we had a while back," and in the Bus Bomb letter he said "What you do not know is whether the death machine is at the sight or whether it is being stored in my basement for future use." So again, taking the Zodiac Killer at face value, we shall look in this region of Cow Hollow or the Marina District for basement residences and flood plains in the region. The 'My Name is..Letter' could easily have been telling the truth also. It was mailed on April 20th talking of "rain we had a while back." San Francisco's rainy months are between November and April, averaging over 100 mm monthly. Here is the chart. If you take a look at this historical monthly and yearly rainfall map of San Francisco, it is evident that December and January were particularly heavy monthly rainfall totals in 1969/70 compared to the average, bearing out the Zodiac's claim of being 'swamped out a while back'. http://ggweather.com/sf/monthly.html
One Zodiac suspect, Rick Marshall, highlighted in the 2007 movie, lived in a basement residence in Scott Street in 1969, a few miles from the crime scene. See here. So if we assume that Zodiac had no car that night, lived nearby and take his statements as true, then logically his escape route from the park was east to low lying ground, vulnerable to flooding, sending him on a collision course with the Marina District of San Francisco or very close by.